From 319d079de3fc95848db4363e578bae9ab37245ed Mon Sep 17 00:00:00 2001
From: Tim Molteno <tim@elec.ac.nz>
Date: Mon, 9 Nov 2026 22:44:43 +1300
Subject: [PATCH 1/4] fix: restore gshank Shanks-tail convergence floor

Issue #131 item 3 raised gshank()'s convergence floor from
denm = 1e-3*den*CRIT to 2e-1*den*CRIT_H, a 200x loosening. On decks
with wires close to a GN 2 ground (radial screen elevated 0.2 m over
epsr 13 / sig 0.005 at 2.7 MHz) the truncated Shanks tail degrades the
Sommerfeld tables until rom2() can never meet its RX = 1e-4 Romberg
test: the integration doubles to the 65536-subdivision cap at every
step, emits an endless ROM2 -- STEP SIZE LIMITED stream (GB/minute)
and effectively never terminates.

Restore the floor to 1e-3*den*CRIT_H while keeping the milder
CRIT_H = 1.1e-4 tail-test scaling. Output is byte-identical (modulo
timing lines) to the pre-loosening build on sommerfeld2/3 and
bruce_sommerfeld; the regression deck now completes in ~14 ms and
agrees with nec2c (13.906 - j445.84 ohm).

Regression decks: testharness/data/wire_order_normal.nec and
wire_order_reversed.nec (the issue #139 wire-order invariance
geometry, which also failed with the loosened floor).
---
 src/c_evlcom.cpp                         | 19 ++++++++++++-------
 testharness/data/wire_order_normal.nec   | 12 ++++++++++++
 testharness/data/wire_order_reversed.nec | 12 ++++++++++++
 3 files changed, 36 insertions(+), 7 deletions(-)
 create mode 100644 testharness/data/wire_order_normal.nec
 create mode 100644 testharness/data/wire_order_reversed.nec

diff --git a/src/c_evlcom.cpp b/src/c_evlcom.cpp
index 312ce702..0f1c2b54 100644
--- a/src/c_evlcom.cpp
+++ b/src/c_evlcom.cpp
@@ -36,7 +36,9 @@ using namespace std;
    before the step-level tolerance binds. Measured to cut ~1.5% of saoa()
    integrand evaluations per Sommerfeld table with byte-identical output on
    every testharness deck and unchanged agreement with the nec2c/FORTRAN
-   references. */
+   references. The companion change that raised gshank()'s denm floor was
+   reverted (see the denm assignment below) after it broke convergence on
+   decks with wires close to the ground. */
 #define CRIT_H	1.1E-4
 #define	PTP	.6283185308
 #define NTS	4
@@ -181,12 +183,15 @@ void c_evlcom::gshank( nec_complex start, nec_complex dela, nec_complex* sum,
 				den=amg;		
 		} /* for ( i = 0; i < nans; i++ ) */
 		
-		/* Convergence floor for the Shanks test (issue #131 item 3): the
-		   increment is judged against max(|q2|*CRIT_H, denm); at 2.e-1 of
-		   the largest accelerated term the loop stops once the increment
-		   has stalled relative to the tail, instead of chasing entries
-		   orders of magnitude smaller than the answer. */
-		denm=2.e-1*den*CRIT_H;
+		/* Convergence floor for the Shanks test: the increment is judged
+		   against max(|q2|*CRIT_H, denm) with denm at 1.e-3 of the largest
+		   accelerated term. Issue #131 item 3 initially raised this floor
+		   to 2.e-1, which lets gshank() return while the integrand is still
+		   converging; the resulting errors in the Sommerfeld tables make
+		   rom2()'s Romberg test (rx = 1e-4) unreachable for decks with
+		   wires close to the ground (e.g. elevated radial screens), so the
+		   integration grinds at the subdivision cap indefinitely. */
+		denm=1.e-3*den*CRIT_H;
 		jm=intx-3;
 		if (jm < 1)
 			jm = 1;
diff --git a/testharness/data/wire_order_normal.nec b/testharness/data/wire_order_normal.nec
new file mode 100644
index 00000000..f6b5c214
--- /dev/null
+++ b/testharness/data/wire_order_normal.nec
@@ -0,0 +1,12 @@
+CM Issue 139 regression: monopole + radial screen over Sommerfeld ground (normal wire order)
+CE
+GW 1 13 0 0 0.2 0 0 12.2 0.025
+GW 2 20 0 0 0.2 20 0 0.2 0.001
+GW 3 20 0 0 0.2 0 20 0.2 0.001
+GE 1
+GN 2,0,0,0,13.,.005
+LD 5 0 0 0 58000000 0 0
+EX 0 1 1 0 1 0
+FR 0 1 0 0 2.7 0
+RP 0 2 1 1001 0 0 89.5 0
+EN
diff --git a/testharness/data/wire_order_reversed.nec b/testharness/data/wire_order_reversed.nec
new file mode 100644
index 00000000..0d05ecde
--- /dev/null
+++ b/testharness/data/wire_order_reversed.nec
@@ -0,0 +1,12 @@
+CM Issue 139 regression: same antenna, reversed wire insertion order
+CE
+GW 3 20 0 0 0.2 0 20 0.2 0.001
+GW 2 20 0 0 0.2 20 0 0.2 0.001
+GW 1 13 0 0 0.2 0 0 12.2 0.025
+GE 1
+GN 2,0,0,0,13.,.005
+LD 5 0 0 0 58000000 0 0
+EX 0 1 1 0 1 0
+FR 0 1 0 0 2.7 0
+RP 0 2 1 1001 0 0 89.5 0
+EN

From 09b96e37b963911c11758c8526e81cfc83bdc476 Mon Sep 17 00:00:00 2001
From: Tim Molteno <tim@elec.ac.nz>
Date: Mon, 9 Nov 2026 22:44:55 +1300
Subject: [PATCH 2/4] test: wire-order invariance regression for Sommerfeld
 interpolation

Add a unit test for github issue #139: a monopole with an explicit
radial screen 0.2 m over a GN 2 Sommerfeld ground, built twice with
the wire cards in natural and reversed order, must give the same
input impedance, accepted power and radiation pattern.

The deck also guards the gshank() convergence floor: with the floor
loosened (issue #131 item 3), rom2() grinds at its subdivision cap
indefinitely and the test fails via the ctest timeout.

Verified against the unfixed c_ggrid::interpolate guard (pre-e3f81e6
inverted branch order): the test fails there, both on the reference
impedance and on order invariance.
---
 src/nec_context_tb.cpp | 79 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/src/nec_context_tb.cpp b/src/nec_context_tb.cpp
index bb2cb584..35d6008e 100644
--- a/src/nec_context_tb.cpp
+++ b/src/nec_context_tb.cpp
@@ -506,3 +506,82 @@ TEST_CASE( "EX type-4 source on a patch centroid zeroes that patch", "[etmns][cu
     REQUIRE(std::real(c1) == Catch::Approx(6.9547e-05).margin(1e-7));
     REQUIRE(std::imag(c1) == Catch::Approx(-1.5977e-05).margin(1e-7));
 }
+
+// ---------------------------------------------------------------------------
+// Issue #139: Sommerfeld interpolation produced wire-order-dependent results.
+//
+// A 12 m monopole with an explicit radial screen 0.2 m above a Sommerfeld
+// ground (GN 2, epsr 13, sig 0.005) is built twice: once in natural wire
+// order and once with the wire cards reversed. The antenna input impedance,
+// accepted power and radiation pattern must not depend on the insertion
+// order.
+//
+// This deck also guards the gshank() Shanks-tail convergence floor: when it
+// was loosened (issue #131 item 3), the Sommerfeld tables degraded enough
+// that rom2() could never meet its Romberg test for this geometry and the
+// simulation ground on at the subdivision cap indefinitely. A regression
+// there shows up as this test hitting the ctest timeout.
+// ---------------------------------------------------------------------------
+namespace {
+	struct issue139_wire {
+		int tag, segments;
+		double x1, y1, z1, x2, y2, z2, radius;
+	};
+
+	void issue139_run(bool reverse_wires,
+		nec_complex& impedance, double& accepted_power, double& horizon_gain_db) {
+		issue139_wire wires[] = {
+			{ 1, 13, 0.0, 0.0, 0.2, 0.0, 0.0, 12.2, 0.025 },
+			{ 2, 20, 0.0, 0.0, 0.2, 20.0, 0.0, 0.2, 0.001 },
+			{ 3, 20, 0.0, 0.0, 0.2, 0.0, 20.0, 0.2, 0.001 },
+		};
+
+		nec_context nec;
+		nec.initialize();
+		c_geometry* geo = nec.get_geometry();
+		for (int i = 0; i < 3; i++) {
+			const issue139_wire& w = wires[reverse_wires ? 2 - i : i];
+			geo->wire(w.tag, w.segments, w.x1, w.y1, w.z1, w.x2, w.y2, w.z2,
+				w.radius, 1.0, 1.0);
+		}
+		nec.geometry_complete(1);
+		nec.gn_card(2, 0, 13.0, 0.005, 0.0, 0.0, 0.0, 0.0);
+		nec.ld_card(5, 0, 0, 0, 58.0e6, 0, 0);
+		nec.fr_card(0, 1, 2.7, 0.0);
+		nec.ex_card(EXCITATION_VOLTAGE, 1, 1, 0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0);
+		nec.rp_card(0, 2, 1, 1, 0, 0, 0, 0.0, 0.0, 89.5, 0.0, 0.0, 0.0);
+
+		impedance = nec_complex(nec.get_impedance_real(0), nec.get_impedance_imag(0));
+		accepted_power = 0.0;
+		nec_antenna_input* ai = nec.get_input_parameters(0);
+		for (unsigned k = 0; k < ai->get_power().size(); k++)
+			accepted_power += ai->get_power()[k];
+
+		nec_radiation_pattern* rp = nec.get_radiation_pattern(0);
+		// theta = 0 is the symmetry null (gain floor sentinel); the 89.5
+		// degree sample (index 1) is the meaningful order-invariance probe.
+		horizon_gain_db = rp->get_gain_tot()[1];
+	}
+}
+
+TEST_CASE("Wire insertion order does not change Sommerfeld-ground results", "[issue139][sommerfeld]") {
+	nec_complex z_forward(0.0, 0.0), z_reverse(0.0, 0.0);
+	double p_forward = 0.0, p_reverse = 0.0;
+	double g_forward = 0.0, g_reverse = 0.0;
+
+	issue139_run(false, z_forward, p_forward, g_forward);
+	issue139_run(true, z_reverse, p_reverse, g_reverse);
+
+	// Reference values (cross-validated against the nec2c reference engine,
+	// which prints 1.3906E+01 -4.4584E+02 for this deck).
+	REQUIRE(std::real(z_forward) == Catch::Approx(13.906).margin(1e-2));
+	REQUIRE(std::imag(z_forward) == Catch::Approx(-445.84).margin(1e-1));
+
+	// Order invariance: the two runs share identical arithmetic up to the
+	// segment numbering, so the comparison can be tight.
+	REQUIRE(std::abs(z_forward - z_reverse)
+		<= 1e-8 * std::max(std::abs(z_forward), std::abs(z_reverse)));
+	REQUIRE(std::abs(p_forward - p_reverse)
+		<= 1e-8 * std::max(std::abs(p_forward), std::abs(p_reverse)));
+	REQUIRE(std::abs(g_forward - g_reverse) < 1e-6);
+}

From 843d2351f9fa1c3e002d0037e2c910b03eda3b39 Mon Sep 17 00:00:00 2001
From: Tim Molteno <tim@elec.ac.nz>
Date: Mon, 9 Nov 2026 22:44:55 +1300
Subject: [PATCH 3/4] fix: nec2diff negative-value comparison, exit status and
 argc guard

Fixes github issue #138.

The real-valued diff() in BaseInput.h tested signed values against
the near-zero floor ((a < 1e-8) && (b < 1e-8)), so any two negative
numbers compared equal: a 178 ohm negative-reactance change or a
-1.71 -> -9.71 dBi gain change reported Difference = 0. A pure sign
flip divided by |a+b| = 0 and printed inf. Both diff() overloads now
normalize by the larger magnitude (|a-b| / max(|a|,|b|)), keeping the
near-zero early-out but keyed on absolute values.

The metric is close to twice the old |a-b|/|a+b| for near-equal
values, so the equalto() thresholds (sum <= 1e-4) now bind about
twice as tightly and previously hidden last-digit engine
discrepancies are visible in nec2diff output.

main() now tracks a flag across the three sections and returns 1 if
any section differs (0 for identical files), so scripts and harnesses
can rely on the exit status. With fewer than two arguments nec2diff
prints usage and returns 1 instead of throwing std::logic_error from
a null std::string construction.

The four reporter cases report 0.994, 0.824, 0.167 (positive control)
and a finite 2.0, matching the issue's suggested-fix values.
Regression fixtures and an exit-code test live in tests/data/issue138/
(ctest necpp_nec2diff_issue138); testharness/data/short_dipole.nec is
the fixture deck.
---
 nec2diff.1                                  |   5 +
 src/BaseInput.h                             |  29 ++--
 src/necDiff.cpp                             |  21 ++-
 testharness/data/short_dipole.nec           |   8 +
 tests/CMakeLists.txt                        |  10 +-
 tests/data/issue138/issue138_base.out       | 158 ++++++++++++++++++++
 tests/data/issue138/issue138_gain.out       | 158 ++++++++++++++++++++
 tests/data/issue138/issue138_reactance.out  | 158 ++++++++++++++++++++
 tests/data/issue138/issue138_resistance.out | 158 ++++++++++++++++++++
 tests/data/issue138/issue138_signflip.out   | 158 ++++++++++++++++++++
 tests/nec2diff_test.cmake                   |  62 ++++++++
 11 files changed, 900 insertions(+), 25 deletions(-)
 create mode 100644 testharness/data/short_dipole.nec
 create mode 100644 tests/data/issue138/issue138_base.out
 create mode 100644 tests/data/issue138/issue138_gain.out
 create mode 100644 tests/data/issue138/issue138_reactance.out
 create mode 100644 tests/data/issue138/issue138_resistance.out
 create mode 100644 tests/data/issue138/issue138_signflip.out
 create mode 100644 tests/nec2diff_test.cmake

diff --git a/nec2diff.1 b/nec2diff.1
index c84c95a9..e70647ab 100644
--- a/nec2diff.1
+++ b/nec2diff.1
@@ -6,10 +6,15 @@ antennas using the Method of Moments.
 
 .SH SYNOPSIS
 .B nec2diff
+.I file_a file_b
 
 .SH DESCRIPTION
 .B nec2diff
 evaluates differences between 2 result files given as parameters.
 
+.SH EXIT STATUS
+nec2diff returns 0 if no differences were found, and 1 if the files differ.
+With fewer than two arguments it prints a usage line and returns 1.
+
 .SH AUTHOR
 nec2diff was written by Tim Molteno <tim@physics.otago.ac.nz>
diff --git a/src/BaseInput.h b/src/BaseInput.h
index 6b45ca8b..d0205262 100644
--- a/src/BaseInput.h
+++ b/src/BaseInput.h
@@ -19,23 +19,24 @@
 
 #include "math_util.h"
 
+#include <algorithm>
+#include <cmath>
 #include <fstream>
 #include <sstream>
 
+/* Relative difference of two values, normalised by the larger magnitude.
+   The scale test must use magnitudes: comparing signed values against the
+   1e-8 floor treats any two negative numbers as "effectively zero". */
 nec_float diff(nec_float a, nec_float b)
 {
 	if (a == b)
 		return 0;
-	if ((a < 1e-8) && (b < 1e-8))
+
+	nec_float scale = std::max(std::fabs(a), std::fabs(b));
+	if (scale < 1e-8)
 		return 0;
 
-	nec_float sub = a - b;
-	nec_float sum = a + b;
-	
-	nec_float ret = sub*sub;
-	if ((a != 0) && (b != 0))
-		ret /= sum*sum;
-	ret = sqrt(ret);
+	nec_float ret = std::fabs(a - b) / scale;
 	if (ret > 1e-2)
 	{
 		cout << "    diff(" << a << "," << b << ") = " << ret << endl;
@@ -47,16 +48,12 @@ nec_float diff(nec_complex a, nec_complex b)
 {
 	if (a == b)
 		return 0;
-	if ((abs(a) < 1e-8) && (abs(b) < 1e-8))
+
+	nec_float scale = std::max(abs(a), abs(b));
+	if (scale < 1e-8)
 		return 0;
 
-	nec_float ret = norm(a - b);
-	nec_float sum = norm(a + b);
-	
-	if (sum != 0)
-		ret /= sum;
-		
-	ret = sqrt(ret);
+	nec_float ret = abs(a - b) / scale;
 	if (ret > 1e-2)
 	{
 		stringstream ss;
diff --git a/src/necDiff.cpp b/src/necDiff.cpp
index 25486e74..d3b0ffe5 100644
--- a/src/necDiff.cpp
+++ b/src/necDiff.cpp
@@ -40,10 +40,12 @@ using namespace std;
 
 int main(int argc, char** argv) {
 
-  if (argc < 2) {
-    cout << "Usage: nec2diff fila, file b" << endl;
+  if (argc < 3) {
+    cout << "Usage: nec2diff file_a file_b" << endl;
+    return 1;
   }
-  cout << "NecDiff 0.12" << endl;
+
+  cout << "NecDiff 0.13" << endl;
 
   string file1(argv[1]);
   string file2(argv[2]);
@@ -51,17 +53,20 @@ int main(int argc, char** argv) {
   cout << "File1: " << file1 << endl;
   cout << "File2: " << file2 << endl;
 
+  bool same = true;
+
   {
     AntennaInput ai1(file1);
     AntennaInput ai2(file2);
 
     cout << "AntennaInput Difference = " << ai1.difference(ai2) << endl;
     if (!ai1.equalto(ai2)) {
+      same = false;
       cerr << file1 << "::" << file2;
       cerr << ". Input Parameters Different " << ai1.difference(ai2) <<  endl;
     }
   }
-  
+
   // Compare Power Budget
 
   {
@@ -70,9 +75,9 @@ int main(int argc, char** argv) {
 
     cout << "PowerBudget Difference = " << r1.difference(r2) << endl;
     if (!r1.equalto(r2)) {
+      same = false;
       cerr << file1 << "::" << file2;
       cerr << ". Power Budgets Different " << r1.difference(r2) << endl;
-      // return 1;
     }
   }
 
@@ -83,13 +88,13 @@ int main(int argc, char** argv) {
 
     cout << "RadiationInput Difference = " << r1.difference(r2) << endl;
     if (!r1.equalto(r2)) {
+      same = false;
       cerr << file1 << "::" << file2;
       cerr << ". Radiation Patterns Different " << r1.difference(r2) << endl;
-      // return 1;
     }
   }
-  
-  return 0;
+
+  return same ? 0 : 1;
 }
 
 
diff --git a/testharness/data/short_dipole.nec b/testharness/data/short_dipole.nec
new file mode 100644
index 00000000..d2ec8161
--- /dev/null
+++ b/testharness/data/short_dipole.nec
@@ -0,0 +1,8 @@
+CM Short (capacitive) 20 m dipole in free space
+CE
+GW 1 21 0 -4.5 0 0 4.5 0 0.001
+GE 0
+EX 0 1 11 0 1 0
+FR 0 1 0 0 14.2 0
+RP 0 1 3 1000 90 0 0 45
+EN
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 2f821508..976759a2 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -99,4 +99,12 @@ add_test(NAME necpp_smoke_hertzian_dipole
     COMMAND ${CMAKE_COMMAND}
         -DNEC2PP=$<TARGET_FILE:nec2++>
         -DINPUT=${CMAKE_SOURCE_DIR}/testharness/data/herzian_dipole.nec
-        -P ${CMAKE_CURRENT_SOURCE_DIR}/smoke_test.cmake)
\ No newline at end of file
+        -P ${CMAKE_CURRENT_SOURCE_DIR}/smoke_test.cmake)
+
+# nec2diff behaviour regression (issue #138): negative-value comparison,
+# finite sign-flip differences, exit statuses and the argc guard.
+add_test(NAME necpp_nec2diff_issue138
+    COMMAND ${CMAKE_COMMAND}
+        -DNEC2DIFF=$<TARGET_FILE:nec2diff>
+        -DDATA_DIR=${CMAKE_CURRENT_SOURCE_DIR}/data/issue138
+        -P ${CMAKE_CURRENT_SOURCE_DIR}/nec2diff_test.cmake)
\ No newline at end of file
diff --git a/tests/data/issue138/issue138_base.out b/tests/data/issue138/issue138_base.out
new file mode 100644
index 00000000..46d63be9
--- /dev/null
+++ b/tests/data/issue138/issue138_base.out
@@ -0,0 +1,158 @@
+
+
+
+                                __________________________________________
+                               |                                          |
+                               | NUMERICAL ELECTROMAGNETICS CODE (nec2++) |
+                               | Implemented in 'C++' in Double Precision |
+                               |        Version 2.3.4 [2026-11-09]        |
+                               |__________________________________________|
+
+
+
+                               ---------------- COMMENTS ----------------
+                                Short (capacitive) 20 m dipole in free space
+                               
+
+
+
+                                -------- STRUCTURE SPECIFICATION --------
+                                COORDINATES MUST BE INPUT IN
+                                METERS OR BE SCALED TO METERS
+                                BEFORE STRUCTURE INPUT IS ENDED
+  WIRE                                                                                 SEG FIRST  LAST  TAG
+   No:        X1         Y1         Z1         X2         Y2         Z2       RADIUS   No:   SEG   SEG  No:
+
+     1      0.0000    -4.5000     0.0000     0.0000     4.5000     0.0000     0.0010    21     1    21    1
+
+     TOTAL SEGMENTS USED: 21   SEGMENTS IN A SYMMETRIC CELL: 21   SYMMETRY FLAG: 0
+
+
+                               ---------- SEGMENTATION DATA ----------
+                                        COORDINATES IN METERS
+                            I+ AND I- INDICATE THE SEGMENTS BEFORE AND AFTER I
+
+   SEG    COORDINATES OF SEGM CENTER     SEGM    ORIENTATION ANGLES    WIRE    CONNECTION DATA   TAG
+   No:       X         Y         Z      LENGTH     ALPHA      BETA    RADIUS    I-     I    I+   NO:
+     1    0.0000   -4.2857    0.0000    0.4286    0.0000   90.0000    0.0010     0     1     2     1
+     2    0.0000   -3.8571    0.0000    0.4286    0.0000   90.0000    0.0010     1     2     3     1
+     3    0.0000   -3.4286    0.0000    0.4286    0.0000   90.0000    0.0010     2     3     4     1
+     4    0.0000   -3.0000    0.0000    0.4286    0.0000   90.0000    0.0010     3     4     5     1
+     5    0.0000   -2.5714    0.0000    0.4286    0.0000   90.0000    0.0010     4     5     6     1
+     6    0.0000   -2.1429    0.0000    0.4286    0.0000   90.0000    0.0010     5     6     7     1
+     7    0.0000   -1.7143    0.0000    0.4286    0.0000   90.0000    0.0010     6     7     8     1
+     8    0.0000   -1.2857    0.0000    0.4286    0.0000   90.0000    0.0010     7     8     9     1
+     9    0.0000   -0.8571    0.0000    0.4286    0.0000   90.0000    0.0010     8     9    10     1
+    10    0.0000   -0.4286    0.0000    0.4286    0.0000   90.0000    0.0010     9    10    11     1
+    11    0.0000   -0.0000    0.0000    0.4286    0.0000   90.0000    0.0010    10    11    12     1
+    12    0.0000    0.4286    0.0000    0.4286    0.0000   90.0000    0.0010    11    12    13     1
+    13    0.0000    0.8571    0.0000    0.4286    0.0000   90.0000    0.0010    12    13    14     1
+    14    0.0000    1.2857    0.0000    0.4286    0.0000   90.0000    0.0010    13    14    15     1
+    15    0.0000    1.7143    0.0000    0.4286    0.0000   90.0000    0.0010    14    15    16     1
+    16    0.0000    2.1429    0.0000    0.4286    0.0000   90.0000    0.0010    15    16    17     1
+    17    0.0000    2.5714    0.0000    0.4286    0.0000   90.0000    0.0010    16    17    18     1
+    18    0.0000    3.0000    0.0000    0.4286    0.0000   90.0000    0.0010    17    18    19     1
+    19    0.0000    3.4286    0.0000    0.4286    0.0000   90.0000    0.0010    18    19    20     1
+    20    0.0000    3.8571    0.0000    0.4286    0.0000   90.0000    0.0010    19    20    21     1
+    21    0.0000    4.2857    0.0000    0.4286    0.0000   90.0000    0.0010    20    21     0     1
+
+
+
+*****  DATA CARD N0.   1 EX   0     1    11     0  1.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   2 FR   0     1     0     0  1.42000E+01  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   3 RP   0     1     3  1000  9.00000E+01  0.00000E+00  0.00000E+00  4.50000E+01  0.00000E+00  0.00000E+00
+
+
+                               --------- FREQUENCY --------
+                               FREQUENCY=  1.4200E+01 MHZ
+                               WAVELENGTH= 2.1112E+01 METERS
+
+
+                        APPROXIMATE INTEGRATION EMPLOYED FOR SEGMENTS
+                        THAT ARE MORE THAN 1.000 WAVELENGTHS APART
+
+
+
+                          ------ STRUCTURE IMPEDANCE LOADING ------
+                                 THIS STRUCTURE IS NOT LOADED
+
+
+
+                            -------- ANTENNA ENVIRONMENT --------
+                            FREE SPACE
+
+
+
+                             ---------- MATRIX TIMING ----------
+                               FILL= 0 msec  FACTOR: 0 msec
+
+
+                      ----- ANTENNA INPUT PARAMETERS -----
+  TAG   SEG       VOLTAGE (VOLTS)         CURRENT (AMPS)         IMPEDANCE (OHMS)        ADMITTANCE (MHOS)     POWER
+  NO.   NO.     REAL      IMAGINARY     REAL      IMAGINARY     REAL      IMAGINARY    REAL       IMAGINARY   (WATTS)
+   1    11  1.0000E+00  0.0000E+00  1.4390E-03  5.1742E-03  4.9889E+01 -1.7939E+02  1.4390E-03  5.1742E-03  7.1948E-04
+
+
+
+
+
+
+
+                        ----- CURRENTS AND LOCATION -----
+                            DISTANCES IN WAVELENGTHS 
+
+   SEG  TAG    COORDINATES OF SEGM CENTER     SEGM    ------------- CURRENT (AMPS) -------------
+   No:  No:       X         Y         Z      LENGTH     REAL      IMAGINARY    MAGN        PHASE
+     1    1    0.0000   -0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+     2    1    0.0000   -0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+     3    1    0.0000   -0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+     4    1    0.0000   -0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+     5    1    0.0000   -0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+     6    1    0.0000   -0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+     7    1    0.0000   -0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+     8    1    0.0000   -0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+     9    1    0.0000   -0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    10    1    0.0000   -0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    11    1    0.0000   -0.0000    0.0000   0.02030  1.4390E-03  5.1742E-03  5.3706E-03   74.459 
+    12    1    0.0000    0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    13    1    0.0000    0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    14    1    0.0000    0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+    15    1    0.0000    0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+    16    1    0.0000    0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+    17    1    0.0000    0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+    18    1    0.0000    0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+    19    1    0.0000    0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+    20    1    0.0000    0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+    21    1    0.0000    0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+
+
+
+
+
+
+                               ---------- POWER BUDGET ---------
+                               INPUT POWER   =  7.1948E-04 Watts
+                               RADIATED POWER=  7.1948E-04 Watts
+                               STRUCTURE LOSS=  0.0000E+00 Watts
+                               NETWORK LOSS  =  0.0000E+00 Watts
+                               EFFICIENCY    =  100.00 Percent
+
+
+                         ----- RADIATION PATTERNS -----
+ ---- ANGLES -----     ----- POWER GAINS -----       ---- POLARIZATION ----   ---- E(THETA) ----    ----- E(PHI) ------
+  THETA      PHI       VERTC   HORIZ   TOTAL       AXIAL      TILT  SENSE   MAGNITUDE    PHASE    MAGNITUDE     PHASE
+ DEGREES   DEGREES        DB       DB       DB       RATIO   DEGREES            VOLTS/M   DEGREES     VOLTS/M   DEGREES
+   90.00      0.00   -999.99     2.04     2.04      0.0000    -90.00 LINEAR  0.0000E+00    180.00  2.6280E-01    -16.78
+   90.00     45.00   -999.99    -1.71    -1.71      0.0000    -90.00 LINEAR  8.7035E-13    163.29  1.7054E-01    -16.71
+   90.00     90.00   -999.99  -999.99  -999.99      0.0000      0.00         1.1274E-12    163.36  1.1274E-12    163.36
+
+
+
+
+
+
+
+
+*****  DATA CARD N0.   4 EN   0     0     0     0  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+
+  TOTAL RUN TIME: 0 msec
\ No newline at end of file
diff --git a/tests/data/issue138/issue138_gain.out b/tests/data/issue138/issue138_gain.out
new file mode 100644
index 00000000..b4d749a6
--- /dev/null
+++ b/tests/data/issue138/issue138_gain.out
@@ -0,0 +1,158 @@
+
+
+
+                                __________________________________________
+                               |                                          |
+                               | NUMERICAL ELECTROMAGNETICS CODE (nec2++) |
+                               | Implemented in 'C++' in Double Precision |
+                               |        Version 2.3.4 [2026-11-09]        |
+                               |__________________________________________|
+
+
+
+                               ---------------- COMMENTS ----------------
+                                Short (capacitive) 20 m dipole in free space
+                               
+
+
+
+                                -------- STRUCTURE SPECIFICATION --------
+                                COORDINATES MUST BE INPUT IN
+                                METERS OR BE SCALED TO METERS
+                                BEFORE STRUCTURE INPUT IS ENDED
+  WIRE                                                                                 SEG FIRST  LAST  TAG
+   No:        X1         Y1         Z1         X2         Y2         Z2       RADIUS   No:   SEG   SEG  No:
+
+     1      0.0000    -4.5000     0.0000     0.0000     4.5000     0.0000     0.0010    21     1    21    1
+
+     TOTAL SEGMENTS USED: 21   SEGMENTS IN A SYMMETRIC CELL: 21   SYMMETRY FLAG: 0
+
+
+                               ---------- SEGMENTATION DATA ----------
+                                        COORDINATES IN METERS
+                            I+ AND I- INDICATE THE SEGMENTS BEFORE AND AFTER I
+
+   SEG    COORDINATES OF SEGM CENTER     SEGM    ORIENTATION ANGLES    WIRE    CONNECTION DATA   TAG
+   No:       X         Y         Z      LENGTH     ALPHA      BETA    RADIUS    I-     I    I+   NO:
+     1    0.0000   -4.2857    0.0000    0.4286    0.0000   90.0000    0.0010     0     1     2     1
+     2    0.0000   -3.8571    0.0000    0.4286    0.0000   90.0000    0.0010     1     2     3     1
+     3    0.0000   -3.4286    0.0000    0.4286    0.0000   90.0000    0.0010     2     3     4     1
+     4    0.0000   -3.0000    0.0000    0.4286    0.0000   90.0000    0.0010     3     4     5     1
+     5    0.0000   -2.5714    0.0000    0.4286    0.0000   90.0000    0.0010     4     5     6     1
+     6    0.0000   -2.1429    0.0000    0.4286    0.0000   90.0000    0.0010     5     6     7     1
+     7    0.0000   -1.7143    0.0000    0.4286    0.0000   90.0000    0.0010     6     7     8     1
+     8    0.0000   -1.2857    0.0000    0.4286    0.0000   90.0000    0.0010     7     8     9     1
+     9    0.0000   -0.8571    0.0000    0.4286    0.0000   90.0000    0.0010     8     9    10     1
+    10    0.0000   -0.4286    0.0000    0.4286    0.0000   90.0000    0.0010     9    10    11     1
+    11    0.0000   -0.0000    0.0000    0.4286    0.0000   90.0000    0.0010    10    11    12     1
+    12    0.0000    0.4286    0.0000    0.4286    0.0000   90.0000    0.0010    11    12    13     1
+    13    0.0000    0.8571    0.0000    0.4286    0.0000   90.0000    0.0010    12    13    14     1
+    14    0.0000    1.2857    0.0000    0.4286    0.0000   90.0000    0.0010    13    14    15     1
+    15    0.0000    1.7143    0.0000    0.4286    0.0000   90.0000    0.0010    14    15    16     1
+    16    0.0000    2.1429    0.0000    0.4286    0.0000   90.0000    0.0010    15    16    17     1
+    17    0.0000    2.5714    0.0000    0.4286    0.0000   90.0000    0.0010    16    17    18     1
+    18    0.0000    3.0000    0.0000    0.4286    0.0000   90.0000    0.0010    17    18    19     1
+    19    0.0000    3.4286    0.0000    0.4286    0.0000   90.0000    0.0010    18    19    20     1
+    20    0.0000    3.8571    0.0000    0.4286    0.0000   90.0000    0.0010    19    20    21     1
+    21    0.0000    4.2857    0.0000    0.4286    0.0000   90.0000    0.0010    20    21     0     1
+
+
+
+*****  DATA CARD N0.   1 EX   0     1    11     0  1.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   2 FR   0     1     0     0  1.42000E+01  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   3 RP   0     1     3  1000  9.00000E+01  0.00000E+00  0.00000E+00  4.50000E+01  0.00000E+00  0.00000E+00
+
+
+                               --------- FREQUENCY --------
+                               FREQUENCY=  1.4200E+01 MHZ
+                               WAVELENGTH= 2.1112E+01 METERS
+
+
+                        APPROXIMATE INTEGRATION EMPLOYED FOR SEGMENTS
+                        THAT ARE MORE THAN 1.000 WAVELENGTHS APART
+
+
+
+                          ------ STRUCTURE IMPEDANCE LOADING ------
+                                 THIS STRUCTURE IS NOT LOADED
+
+
+
+                            -------- ANTENNA ENVIRONMENT --------
+                            FREE SPACE
+
+
+
+                             ---------- MATRIX TIMING ----------
+                               FILL= 0 msec  FACTOR: 0 msec
+
+
+                      ----- ANTENNA INPUT PARAMETERS -----
+  TAG   SEG       VOLTAGE (VOLTS)         CURRENT (AMPS)         IMPEDANCE (OHMS)        ADMITTANCE (MHOS)     POWER
+  NO.   NO.     REAL      IMAGINARY     REAL      IMAGINARY     REAL      IMAGINARY    REAL       IMAGINARY   (WATTS)
+   1    11  1.0000E+00  0.0000E+00  1.4390E-03  5.1742E-03  4.9889E+01 -1.7939E+02  1.4390E-03  5.1742E-03  7.1948E-04
+
+
+
+
+
+
+
+                        ----- CURRENTS AND LOCATION -----
+                            DISTANCES IN WAVELENGTHS 
+
+   SEG  TAG    COORDINATES OF SEGM CENTER     SEGM    ------------- CURRENT (AMPS) -------------
+   No:  No:       X         Y         Z      LENGTH     REAL      IMAGINARY    MAGN        PHASE
+     1    1    0.0000   -0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+     2    1    0.0000   -0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+     3    1    0.0000   -0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+     4    1    0.0000   -0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+     5    1    0.0000   -0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+     6    1    0.0000   -0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+     7    1    0.0000   -0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+     8    1    0.0000   -0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+     9    1    0.0000   -0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    10    1    0.0000   -0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    11    1    0.0000   -0.0000    0.0000   0.02030  1.4390E-03  5.1742E-03  5.3706E-03   74.459 
+    12    1    0.0000    0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    13    1    0.0000    0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    14    1    0.0000    0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+    15    1    0.0000    0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+    16    1    0.0000    0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+    17    1    0.0000    0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+    18    1    0.0000    0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+    19    1    0.0000    0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+    20    1    0.0000    0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+    21    1    0.0000    0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+
+
+
+
+
+
+                               ---------- POWER BUDGET ---------
+                               INPUT POWER   =  7.1948E-04 Watts
+                               RADIATED POWER=  7.1948E-04 Watts
+                               STRUCTURE LOSS=  0.0000E+00 Watts
+                               NETWORK LOSS  =  0.0000E+00 Watts
+                               EFFICIENCY    =  100.00 Percent
+
+
+                         ----- RADIATION PATTERNS -----
+ ---- ANGLES -----     ----- POWER GAINS -----       ---- POLARIZATION ----   ---- E(THETA) ----    ----- E(PHI) ------
+  THETA      PHI       VERTC   HORIZ   TOTAL       AXIAL      TILT  SENSE   MAGNITUDE    PHASE    MAGNITUDE     PHASE
+ DEGREES   DEGREES        DB       DB       DB       RATIO   DEGREES            VOLTS/M   DEGREES     VOLTS/M   DEGREES
+   90.00      0.00   -999.99     2.04     2.04      0.0000    -90.00 LINEAR  0.0000E+00    180.00  2.6280E-01    -16.78
+   90.00     45.00   -999.99    -9.71    -9.71      0.0000    -90.00 LINEAR  8.7035E-13    163.29  1.7054E-01    -16.71
+   90.00     90.00   -999.99  -999.99  -999.99      0.0000      0.00         1.1274E-12    163.36  1.1274E-12    163.36
+
+
+
+
+
+
+
+
+*****  DATA CARD N0.   4 EN   0     0     0     0  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+
+  TOTAL RUN TIME: 0 msec
\ No newline at end of file
diff --git a/tests/data/issue138/issue138_reactance.out b/tests/data/issue138/issue138_reactance.out
new file mode 100644
index 00000000..2a352e7b
--- /dev/null
+++ b/tests/data/issue138/issue138_reactance.out
@@ -0,0 +1,158 @@
+
+
+
+                                __________________________________________
+                               |                                          |
+                               | NUMERICAL ELECTROMAGNETICS CODE (nec2++) |
+                               | Implemented in 'C++' in Double Precision |
+                               |        Version 2.3.4 [2026-11-09]        |
+                               |__________________________________________|
+
+
+
+                               ---------------- COMMENTS ----------------
+                                Short (capacitive) 20 m dipole in free space
+                               
+
+
+
+                                -------- STRUCTURE SPECIFICATION --------
+                                COORDINATES MUST BE INPUT IN
+                                METERS OR BE SCALED TO METERS
+                                BEFORE STRUCTURE INPUT IS ENDED
+  WIRE                                                                                 SEG FIRST  LAST  TAG
+   No:        X1         Y1         Z1         X2         Y2         Z2       RADIUS   No:   SEG   SEG  No:
+
+     1      0.0000    -4.5000     0.0000     0.0000     4.5000     0.0000     0.0010    21     1    21    1
+
+     TOTAL SEGMENTS USED: 21   SEGMENTS IN A SYMMETRIC CELL: 21   SYMMETRY FLAG: 0
+
+
+                               ---------- SEGMENTATION DATA ----------
+                                        COORDINATES IN METERS
+                            I+ AND I- INDICATE THE SEGMENTS BEFORE AND AFTER I
+
+   SEG    COORDINATES OF SEGM CENTER     SEGM    ORIENTATION ANGLES    WIRE    CONNECTION DATA   TAG
+   No:       X         Y         Z      LENGTH     ALPHA      BETA    RADIUS    I-     I    I+   NO:
+     1    0.0000   -4.2857    0.0000    0.4286    0.0000   90.0000    0.0010     0     1     2     1
+     2    0.0000   -3.8571    0.0000    0.4286    0.0000   90.0000    0.0010     1     2     3     1
+     3    0.0000   -3.4286    0.0000    0.4286    0.0000   90.0000    0.0010     2     3     4     1
+     4    0.0000   -3.0000    0.0000    0.4286    0.0000   90.0000    0.0010     3     4     5     1
+     5    0.0000   -2.5714    0.0000    0.4286    0.0000   90.0000    0.0010     4     5     6     1
+     6    0.0000   -2.1429    0.0000    0.4286    0.0000   90.0000    0.0010     5     6     7     1
+     7    0.0000   -1.7143    0.0000    0.4286    0.0000   90.0000    0.0010     6     7     8     1
+     8    0.0000   -1.2857    0.0000    0.4286    0.0000   90.0000    0.0010     7     8     9     1
+     9    0.0000   -0.8571    0.0000    0.4286    0.0000   90.0000    0.0010     8     9    10     1
+    10    0.0000   -0.4286    0.0000    0.4286    0.0000   90.0000    0.0010     9    10    11     1
+    11    0.0000   -0.0000    0.0000    0.4286    0.0000   90.0000    0.0010    10    11    12     1
+    12    0.0000    0.4286    0.0000    0.4286    0.0000   90.0000    0.0010    11    12    13     1
+    13    0.0000    0.8571    0.0000    0.4286    0.0000   90.0000    0.0010    12    13    14     1
+    14    0.0000    1.2857    0.0000    0.4286    0.0000   90.0000    0.0010    13    14    15     1
+    15    0.0000    1.7143    0.0000    0.4286    0.0000   90.0000    0.0010    14    15    16     1
+    16    0.0000    2.1429    0.0000    0.4286    0.0000   90.0000    0.0010    15    16    17     1
+    17    0.0000    2.5714    0.0000    0.4286    0.0000   90.0000    0.0010    16    17    18     1
+    18    0.0000    3.0000    0.0000    0.4286    0.0000   90.0000    0.0010    17    18    19     1
+    19    0.0000    3.4286    0.0000    0.4286    0.0000   90.0000    0.0010    18    19    20     1
+    20    0.0000    3.8571    0.0000    0.4286    0.0000   90.0000    0.0010    19    20    21     1
+    21    0.0000    4.2857    0.0000    0.4286    0.0000   90.0000    0.0010    20    21     0     1
+
+
+
+*****  DATA CARD N0.   1 EX   0     1    11     0  1.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   2 FR   0     1     0     0  1.42000E+01  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   3 RP   0     1     3  1000  9.00000E+01  0.00000E+00  0.00000E+00  4.50000E+01  0.00000E+00  0.00000E+00
+
+
+                               --------- FREQUENCY --------
+                               FREQUENCY=  1.4200E+01 MHZ
+                               WAVELENGTH= 2.1112E+01 METERS
+
+
+                        APPROXIMATE INTEGRATION EMPLOYED FOR SEGMENTS
+                        THAT ARE MORE THAN 1.000 WAVELENGTHS APART
+
+
+
+                          ------ STRUCTURE IMPEDANCE LOADING ------
+                                 THIS STRUCTURE IS NOT LOADED
+
+
+
+                            -------- ANTENNA ENVIRONMENT --------
+                            FREE SPACE
+
+
+
+                             ---------- MATRIX TIMING ----------
+                               FILL= 0 msec  FACTOR: 0 msec
+
+
+                      ----- ANTENNA INPUT PARAMETERS -----
+  TAG   SEG       VOLTAGE (VOLTS)         CURRENT (AMPS)         IMPEDANCE (OHMS)        ADMITTANCE (MHOS)     POWER
+  NO.   NO.     REAL      IMAGINARY     REAL      IMAGINARY     REAL      IMAGINARY    REAL       IMAGINARY   (WATTS)
+   1    11  1.0000E+00  0.0000E+00  1.4390E-03  5.1742E-03  4.9889E+01 -1.0000E+00  1.4390E-03  5.1742E-03  7.1948E-04
+
+
+
+
+
+
+
+                        ----- CURRENTS AND LOCATION -----
+                            DISTANCES IN WAVELENGTHS 
+
+   SEG  TAG    COORDINATES OF SEGM CENTER     SEGM    ------------- CURRENT (AMPS) -------------
+   No:  No:       X         Y         Z      LENGTH     REAL      IMAGINARY    MAGN        PHASE
+     1    1    0.0000   -0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+     2    1    0.0000   -0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+     3    1    0.0000   -0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+     4    1    0.0000   -0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+     5    1    0.0000   -0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+     6    1    0.0000   -0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+     7    1    0.0000   -0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+     8    1    0.0000   -0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+     9    1    0.0000   -0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    10    1    0.0000   -0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    11    1    0.0000   -0.0000    0.0000   0.02030  1.4390E-03  5.1742E-03  5.3706E-03   74.459 
+    12    1    0.0000    0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    13    1    0.0000    0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    14    1    0.0000    0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+    15    1    0.0000    0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+    16    1    0.0000    0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+    17    1    0.0000    0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+    18    1    0.0000    0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+    19    1    0.0000    0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+    20    1    0.0000    0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+    21    1    0.0000    0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+
+
+
+
+
+
+                               ---------- POWER BUDGET ---------
+                               INPUT POWER   =  7.1948E-04 Watts
+                               RADIATED POWER=  7.1948E-04 Watts
+                               STRUCTURE LOSS=  0.0000E+00 Watts
+                               NETWORK LOSS  =  0.0000E+00 Watts
+                               EFFICIENCY    =  100.00 Percent
+
+
+                         ----- RADIATION PATTERNS -----
+ ---- ANGLES -----     ----- POWER GAINS -----       ---- POLARIZATION ----   ---- E(THETA) ----    ----- E(PHI) ------
+  THETA      PHI       VERTC   HORIZ   TOTAL       AXIAL      TILT  SENSE   MAGNITUDE    PHASE    MAGNITUDE     PHASE
+ DEGREES   DEGREES        DB       DB       DB       RATIO   DEGREES            VOLTS/M   DEGREES     VOLTS/M   DEGREES
+   90.00      0.00   -999.99     2.04     2.04      0.0000    -90.00 LINEAR  0.0000E+00    180.00  2.6280E-01    -16.78
+   90.00     45.00   -999.99    -1.71    -1.71      0.0000    -90.00 LINEAR  8.7035E-13    163.29  1.7054E-01    -16.71
+   90.00     90.00   -999.99  -999.99  -999.99      0.0000      0.00         1.1274E-12    163.36  1.1274E-12    163.36
+
+
+
+
+
+
+
+
+*****  DATA CARD N0.   4 EN   0     0     0     0  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+
+  TOTAL RUN TIME: 0 msec
\ No newline at end of file
diff --git a/tests/data/issue138/issue138_resistance.out b/tests/data/issue138/issue138_resistance.out
new file mode 100644
index 00000000..c06866a1
--- /dev/null
+++ b/tests/data/issue138/issue138_resistance.out
@@ -0,0 +1,158 @@
+
+
+
+                                __________________________________________
+                               |                                          |
+                               | NUMERICAL ELECTROMAGNETICS CODE (nec2++) |
+                               | Implemented in 'C++' in Double Precision |
+                               |        Version 2.3.4 [2026-11-09]        |
+                               |__________________________________________|
+
+
+
+                               ---------------- COMMENTS ----------------
+                                Short (capacitive) 20 m dipole in free space
+                               
+
+
+
+                                -------- STRUCTURE SPECIFICATION --------
+                                COORDINATES MUST BE INPUT IN
+                                METERS OR BE SCALED TO METERS
+                                BEFORE STRUCTURE INPUT IS ENDED
+  WIRE                                                                                 SEG FIRST  LAST  TAG
+   No:        X1         Y1         Z1         X2         Y2         Z2       RADIUS   No:   SEG   SEG  No:
+
+     1      0.0000    -4.5000     0.0000     0.0000     4.5000     0.0000     0.0010    21     1    21    1
+
+     TOTAL SEGMENTS USED: 21   SEGMENTS IN A SYMMETRIC CELL: 21   SYMMETRY FLAG: 0
+
+
+                               ---------- SEGMENTATION DATA ----------
+                                        COORDINATES IN METERS
+                            I+ AND I- INDICATE THE SEGMENTS BEFORE AND AFTER I
+
+   SEG    COORDINATES OF SEGM CENTER     SEGM    ORIENTATION ANGLES    WIRE    CONNECTION DATA   TAG
+   No:       X         Y         Z      LENGTH     ALPHA      BETA    RADIUS    I-     I    I+   NO:
+     1    0.0000   -4.2857    0.0000    0.4286    0.0000   90.0000    0.0010     0     1     2     1
+     2    0.0000   -3.8571    0.0000    0.4286    0.0000   90.0000    0.0010     1     2     3     1
+     3    0.0000   -3.4286    0.0000    0.4286    0.0000   90.0000    0.0010     2     3     4     1
+     4    0.0000   -3.0000    0.0000    0.4286    0.0000   90.0000    0.0010     3     4     5     1
+     5    0.0000   -2.5714    0.0000    0.4286    0.0000   90.0000    0.0010     4     5     6     1
+     6    0.0000   -2.1429    0.0000    0.4286    0.0000   90.0000    0.0010     5     6     7     1
+     7    0.0000   -1.7143    0.0000    0.4286    0.0000   90.0000    0.0010     6     7     8     1
+     8    0.0000   -1.2857    0.0000    0.4286    0.0000   90.0000    0.0010     7     8     9     1
+     9    0.0000   -0.8571    0.0000    0.4286    0.0000   90.0000    0.0010     8     9    10     1
+    10    0.0000   -0.4286    0.0000    0.4286    0.0000   90.0000    0.0010     9    10    11     1
+    11    0.0000   -0.0000    0.0000    0.4286    0.0000   90.0000    0.0010    10    11    12     1
+    12    0.0000    0.4286    0.0000    0.4286    0.0000   90.0000    0.0010    11    12    13     1
+    13    0.0000    0.8571    0.0000    0.4286    0.0000   90.0000    0.0010    12    13    14     1
+    14    0.0000    1.2857    0.0000    0.4286    0.0000   90.0000    0.0010    13    14    15     1
+    15    0.0000    1.7143    0.0000    0.4286    0.0000   90.0000    0.0010    14    15    16     1
+    16    0.0000    2.1429    0.0000    0.4286    0.0000   90.0000    0.0010    15    16    17     1
+    17    0.0000    2.5714    0.0000    0.4286    0.0000   90.0000    0.0010    16    17    18     1
+    18    0.0000    3.0000    0.0000    0.4286    0.0000   90.0000    0.0010    17    18    19     1
+    19    0.0000    3.4286    0.0000    0.4286    0.0000   90.0000    0.0010    18    19    20     1
+    20    0.0000    3.8571    0.0000    0.4286    0.0000   90.0000    0.0010    19    20    21     1
+    21    0.0000    4.2857    0.0000    0.4286    0.0000   90.0000    0.0010    20    21     0     1
+
+
+
+*****  DATA CARD N0.   1 EX   0     1    11     0  1.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   2 FR   0     1     0     0  1.42000E+01  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   3 RP   0     1     3  1000  9.00000E+01  0.00000E+00  0.00000E+00  4.50000E+01  0.00000E+00  0.00000E+00
+
+
+                               --------- FREQUENCY --------
+                               FREQUENCY=  1.4200E+01 MHZ
+                               WAVELENGTH= 2.1112E+01 METERS
+
+
+                        APPROXIMATE INTEGRATION EMPLOYED FOR SEGMENTS
+                        THAT ARE MORE THAN 1.000 WAVELENGTHS APART
+
+
+
+                          ------ STRUCTURE IMPEDANCE LOADING ------
+                                 THIS STRUCTURE IS NOT LOADED
+
+
+
+                            -------- ANTENNA ENVIRONMENT --------
+                            FREE SPACE
+
+
+
+                             ---------- MATRIX TIMING ----------
+                               FILL= 0 msec  FACTOR: 0 msec
+
+
+                      ----- ANTENNA INPUT PARAMETERS -----
+  TAG   SEG       VOLTAGE (VOLTS)         CURRENT (AMPS)         IMPEDANCE (OHMS)        ADMITTANCE (MHOS)     POWER
+  NO.   NO.     REAL      IMAGINARY     REAL      IMAGINARY     REAL      IMAGINARY    REAL       IMAGINARY   (WATTS)
+   1    11  1.0000E+00  0.0000E+00  1.4390E-03  5.1742E-03  5.9889E+01 -1.7939E+02  1.4390E-03  5.1742E-03  7.1948E-04
+
+
+
+
+
+
+
+                        ----- CURRENTS AND LOCATION -----
+                            DISTANCES IN WAVELENGTHS 
+
+   SEG  TAG    COORDINATES OF SEGM CENTER     SEGM    ------------- CURRENT (AMPS) -------------
+   No:  No:       X         Y         Z      LENGTH     REAL      IMAGINARY    MAGN        PHASE
+     1    1    0.0000   -0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+     2    1    0.0000   -0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+     3    1    0.0000   -0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+     4    1    0.0000   -0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+     5    1    0.0000   -0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+     6    1    0.0000   -0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+     7    1    0.0000   -0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+     8    1    0.0000   -0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+     9    1    0.0000   -0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    10    1    0.0000   -0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    11    1    0.0000   -0.0000    0.0000   0.02030  1.4390E-03  5.1742E-03  5.3706E-03   74.459 
+    12    1    0.0000    0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    13    1    0.0000    0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    14    1    0.0000    0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+    15    1    0.0000    0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+    16    1    0.0000    0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+    17    1    0.0000    0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+    18    1    0.0000    0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+    19    1    0.0000    0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+    20    1    0.0000    0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+    21    1    0.0000    0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+
+
+
+
+
+
+                               ---------- POWER BUDGET ---------
+                               INPUT POWER   =  7.1948E-04 Watts
+                               RADIATED POWER=  7.1948E-04 Watts
+                               STRUCTURE LOSS=  0.0000E+00 Watts
+                               NETWORK LOSS  =  0.0000E+00 Watts
+                               EFFICIENCY    =  100.00 Percent
+
+
+                         ----- RADIATION PATTERNS -----
+ ---- ANGLES -----     ----- POWER GAINS -----       ---- POLARIZATION ----   ---- E(THETA) ----    ----- E(PHI) ------
+  THETA      PHI       VERTC   HORIZ   TOTAL       AXIAL      TILT  SENSE   MAGNITUDE    PHASE    MAGNITUDE     PHASE
+ DEGREES   DEGREES        DB       DB       DB       RATIO   DEGREES            VOLTS/M   DEGREES     VOLTS/M   DEGREES
+   90.00      0.00   -999.99     2.04     2.04      0.0000    -90.00 LINEAR  0.0000E+00    180.00  2.6280E-01    -16.78
+   90.00     45.00   -999.99    -1.71    -1.71      0.0000    -90.00 LINEAR  8.7035E-13    163.29  1.7054E-01    -16.71
+   90.00     90.00   -999.99  -999.99  -999.99      0.0000      0.00         1.1274E-12    163.36  1.1274E-12    163.36
+
+
+
+
+
+
+
+
+*****  DATA CARD N0.   4 EN   0     0     0     0  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+
+  TOTAL RUN TIME: 0 msec
\ No newline at end of file
diff --git a/tests/data/issue138/issue138_signflip.out b/tests/data/issue138/issue138_signflip.out
new file mode 100644
index 00000000..a2bd38a5
--- /dev/null
+++ b/tests/data/issue138/issue138_signflip.out
@@ -0,0 +1,158 @@
+
+
+
+                                __________________________________________
+                               |                                          |
+                               | NUMERICAL ELECTROMAGNETICS CODE (nec2++) |
+                               | Implemented in 'C++' in Double Precision |
+                               |        Version 2.3.4 [2026-11-09]        |
+                               |__________________________________________|
+
+
+
+                               ---------------- COMMENTS ----------------
+                                Short (capacitive) 20 m dipole in free space
+                               
+
+
+
+                                -------- STRUCTURE SPECIFICATION --------
+                                COORDINATES MUST BE INPUT IN
+                                METERS OR BE SCALED TO METERS
+                                BEFORE STRUCTURE INPUT IS ENDED
+  WIRE                                                                                 SEG FIRST  LAST  TAG
+   No:        X1         Y1         Z1         X2         Y2         Z2       RADIUS   No:   SEG   SEG  No:
+
+     1      0.0000    -4.5000     0.0000     0.0000     4.5000     0.0000     0.0010    21     1    21    1
+
+     TOTAL SEGMENTS USED: 21   SEGMENTS IN A SYMMETRIC CELL: 21   SYMMETRY FLAG: 0
+
+
+                               ---------- SEGMENTATION DATA ----------
+                                        COORDINATES IN METERS
+                            I+ AND I- INDICATE THE SEGMENTS BEFORE AND AFTER I
+
+   SEG    COORDINATES OF SEGM CENTER     SEGM    ORIENTATION ANGLES    WIRE    CONNECTION DATA   TAG
+   No:       X         Y         Z      LENGTH     ALPHA      BETA    RADIUS    I-     I    I+   NO:
+     1    0.0000   -4.2857    0.0000    0.4286    0.0000   90.0000    0.0010     0     1     2     1
+     2    0.0000   -3.8571    0.0000    0.4286    0.0000   90.0000    0.0010     1     2     3     1
+     3    0.0000   -3.4286    0.0000    0.4286    0.0000   90.0000    0.0010     2     3     4     1
+     4    0.0000   -3.0000    0.0000    0.4286    0.0000   90.0000    0.0010     3     4     5     1
+     5    0.0000   -2.5714    0.0000    0.4286    0.0000   90.0000    0.0010     4     5     6     1
+     6    0.0000   -2.1429    0.0000    0.4286    0.0000   90.0000    0.0010     5     6     7     1
+     7    0.0000   -1.7143    0.0000    0.4286    0.0000   90.0000    0.0010     6     7     8     1
+     8    0.0000   -1.2857    0.0000    0.4286    0.0000   90.0000    0.0010     7     8     9     1
+     9    0.0000   -0.8571    0.0000    0.4286    0.0000   90.0000    0.0010     8     9    10     1
+    10    0.0000   -0.4286    0.0000    0.4286    0.0000   90.0000    0.0010     9    10    11     1
+    11    0.0000   -0.0000    0.0000    0.4286    0.0000   90.0000    0.0010    10    11    12     1
+    12    0.0000    0.4286    0.0000    0.4286    0.0000   90.0000    0.0010    11    12    13     1
+    13    0.0000    0.8571    0.0000    0.4286    0.0000   90.0000    0.0010    12    13    14     1
+    14    0.0000    1.2857    0.0000    0.4286    0.0000   90.0000    0.0010    13    14    15     1
+    15    0.0000    1.7143    0.0000    0.4286    0.0000   90.0000    0.0010    14    15    16     1
+    16    0.0000    2.1429    0.0000    0.4286    0.0000   90.0000    0.0010    15    16    17     1
+    17    0.0000    2.5714    0.0000    0.4286    0.0000   90.0000    0.0010    16    17    18     1
+    18    0.0000    3.0000    0.0000    0.4286    0.0000   90.0000    0.0010    17    18    19     1
+    19    0.0000    3.4286    0.0000    0.4286    0.0000   90.0000    0.0010    18    19    20     1
+    20    0.0000    3.8571    0.0000    0.4286    0.0000   90.0000    0.0010    19    20    21     1
+    21    0.0000    4.2857    0.0000    0.4286    0.0000   90.0000    0.0010    20    21     0     1
+
+
+
+*****  DATA CARD N0.   1 EX   0     1    11     0  1.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   2 FR   0     1     0     0  1.42000E+01  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+*****  DATA CARD N0.   3 RP   0     1     3  1000  9.00000E+01  0.00000E+00  0.00000E+00  4.50000E+01  0.00000E+00  0.00000E+00
+
+
+                               --------- FREQUENCY --------
+                               FREQUENCY=  1.4200E+01 MHZ
+                               WAVELENGTH= 2.1112E+01 METERS
+
+
+                        APPROXIMATE INTEGRATION EMPLOYED FOR SEGMENTS
+                        THAT ARE MORE THAN 1.000 WAVELENGTHS APART
+
+
+
+                          ------ STRUCTURE IMPEDANCE LOADING ------
+                                 THIS STRUCTURE IS NOT LOADED
+
+
+
+                            -------- ANTENNA ENVIRONMENT --------
+                            FREE SPACE
+
+
+
+                             ---------- MATRIX TIMING ----------
+                               FILL= 0 msec  FACTOR: 0 msec
+
+
+                      ----- ANTENNA INPUT PARAMETERS -----
+  TAG   SEG       VOLTAGE (VOLTS)         CURRENT (AMPS)         IMPEDANCE (OHMS)        ADMITTANCE (MHOS)     POWER
+  NO.   NO.     REAL      IMAGINARY     REAL      IMAGINARY     REAL      IMAGINARY    REAL       IMAGINARY   (WATTS)
+   1    11  1.0000E+00  0.0000E+00  1.4390E-03  5.1742E-03  4.9889E+01  1.7939E+02  1.4390E-03  5.1742E-03  7.1948E-04
+
+
+
+
+
+
+
+                        ----- CURRENTS AND LOCATION -----
+                            DISTANCES IN WAVELENGTHS 
+
+   SEG  TAG    COORDINATES OF SEGM CENTER     SEGM    ------------- CURRENT (AMPS) -------------
+   No:  No:       X         Y         Z      LENGTH     REAL      IMAGINARY    MAGN        PHASE
+     1    1    0.0000   -0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+     2    1    0.0000   -0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+     3    1    0.0000   -0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+     4    1    0.0000   -0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+     5    1    0.0000   -0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+     6    1    0.0000   -0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+     7    1    0.0000   -0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+     8    1    0.0000   -0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+     9    1    0.0000   -0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    10    1    0.0000   -0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    11    1    0.0000   -0.0000    0.0000   0.02030  1.4390E-03  5.1742E-03  5.3706E-03   74.459 
+    12    1    0.0000    0.0203    0.0000   0.02030  1.4245E-03  5.0021E-03  5.2010E-03   74.104 
+    13    1    0.0000    0.0406    0.0000   0.02030  1.3815E-03  4.7275E-03  4.9252E-03   73.710 
+    14    1    0.0000    0.0609    0.0000   0.02030  1.3105E-03  4.3879E-03  4.5794E-03   73.371 
+    15    1    0.0000    0.0812    0.0000   0.02030  1.2124E-03  3.9826E-03  4.1630E-03   73.068 
+    16    1    0.0000    0.1015    0.0000   0.02030  1.0887E-03  3.5150E-03  3.6798E-03   72.791 
+    17    1    0.0000    0.1218    0.0000   0.02030  9.4093E-04  2.9905E-03  3.1350E-03   72.534 
+    18    1    0.0000    0.1421    0.0000   0.02030  7.7088E-04  2.4146E-03  2.5347E-03   72.294 
+    19    1    0.0000    0.1624    0.0000   0.02030  5.8025E-04  1.7929E-03  1.8845E-03   72.066 
+    20    1    0.0000    0.1827    0.0000   0.02030  3.6996E-04  1.1285E-03  1.1876E-03   71.849 
+    21    1    0.0000    0.2030    0.0000   0.02030  1.3519E-04  4.0742E-04  4.2926E-04   71.643 
+
+
+
+
+
+
+                               ---------- POWER BUDGET ---------
+                               INPUT POWER   =  7.1948E-04 Watts
+                               RADIATED POWER=  7.1948E-04 Watts
+                               STRUCTURE LOSS=  0.0000E+00 Watts
+                               NETWORK LOSS  =  0.0000E+00 Watts
+                               EFFICIENCY    =  100.00 Percent
+
+
+                         ----- RADIATION PATTERNS -----
+ ---- ANGLES -----     ----- POWER GAINS -----       ---- POLARIZATION ----   ---- E(THETA) ----    ----- E(PHI) ------
+  THETA      PHI       VERTC   HORIZ   TOTAL       AXIAL      TILT  SENSE   MAGNITUDE    PHASE    MAGNITUDE     PHASE
+ DEGREES   DEGREES        DB       DB       DB       RATIO   DEGREES            VOLTS/M   DEGREES     VOLTS/M   DEGREES
+   90.00      0.00   -999.99     2.04     2.04      0.0000    -90.00 LINEAR  0.0000E+00    180.00  2.6280E-01    -16.78
+   90.00     45.00   -999.99    -1.71    -1.71      0.0000    -90.00 LINEAR  8.7035E-13    163.29  1.7054E-01    -16.71
+   90.00     90.00   -999.99  -999.99  -999.99      0.0000      0.00         1.1274E-12    163.36  1.1274E-12    163.36
+
+
+
+
+
+
+
+
+*****  DATA CARD N0.   4 EN   0     0     0     0  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00  0.00000E+00
+
+  TOTAL RUN TIME: 0 msec
\ No newline at end of file
diff --git a/tests/nec2diff_test.cmake b/tests/nec2diff_test.cmake
new file mode 100644
index 00000000..5ea04bb2
--- /dev/null
+++ b/tests/nec2diff_test.cmake
@@ -0,0 +1,62 @@
+# Regression test for github issue #138: nec2diff treated any two negative
+# values as equal (the zero-test compared signed values), reported `inf` for
+# pure sign flips, always exited 0, and aborted when called with fewer than
+# two file arguments.
+#
+# The fixtures in data/issue138 are one NEC output file and four single-value
+# edits of it: a negative reactance change (-179.39 -> -1.00 ohm), a negative
+# dB gain change (-1.71 -> -9.71 dBi), a positive control (49.889 -> 59.889
+# ohm) and a reactance sign flip (-179.39 -> +179.39 ohm).
+#
+# Run as:
+#   cmake -DNEC2DIFF=<path> -DDATA_DIR=<dir> -P nec2diff_test.cmake
+
+set(BASE ${DATA_DIR}/issue138_base.out)
+
+# Every edited fixture must be reported as different: exit status 1.
+set(DIFFER_CASES
+    issue138_reactance
+    issue138_gain
+    issue138_resistance
+    issue138_signflip)
+
+foreach(case_name IN LISTS DIFFER_CASES)
+    execute_process(
+        COMMAND ${NEC2DIFF} ${BASE} ${DATA_DIR}/${case_name}.out
+        OUTPUT_VARIABLE nec2diff_stdout
+        ERROR_VARIABLE nec2diff_stderr
+        RESULT_VARIABLE nec2diff_result)
+    if(NOT nec2diff_result EQUAL 1)
+        message(FATAL_ERROR
+            "nec2diff ${case_name}: expected exit status 1 (different), got ${nec2diff_result}\n"
+            "stdout:\n${nec2diff_stdout}\nstderr:\n${nec2diff_stderr}")
+    endif()
+endforeach()
+
+# Identical files must compare equal: exit status 0.
+execute_process(
+    COMMAND ${NEC2DIFF} ${BASE} ${BASE}
+    OUTPUT_QUIET ERROR_QUIET
+    RESULT_VARIABLE nec2diff_result)
+if(NOT nec2diff_result EQUAL 0)
+    message(FATAL_ERROR "nec2diff: identical files must exit 0, got ${nec2diff_result}")
+endif()
+
+# Fewer than two arguments must print usage and exit 1 (not abort).
+execute_process(
+    COMMAND ${NEC2DIFF}
+    OUTPUT_QUIET ERROR_QUIET
+    RESULT_VARIABLE nec2diff_result)
+if(NOT nec2diff_result EQUAL 1)
+    message(FATAL_ERROR "nec2diff: no arguments must exit 1, got ${nec2diff_result}")
+endif()
+
+execute_process(
+    COMMAND ${NEC2DIFF} ${BASE}
+    OUTPUT_QUIET ERROR_QUIET
+    RESULT_VARIABLE nec2diff_result)
+if(NOT nec2diff_result EQUAL 1)
+    message(FATAL_ERROR "nec2diff: one argument must exit 1, got ${nec2diff_result}")
+endif()
+
+message(STATUS "nec2diff issue #138 regression test passed")

From dda4a52953b4b1e02c7abd7fc272198a02f949f7 Mon Sep 17 00:00:00 2001
From: Tim Molteno <tim@elec.ac.nz>
Date: Mon, 9 Nov 2026 22:44:55 +1300
Subject: [PATCH 4/4] docs: document gshank floor revert and nec2diff fixes
 (issues #138, #139)

---
 CHANGELOG.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7c09fee8..6242dbdd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@
 ### Bug Fixes
 * **`zero-current` now maps to signed NEC `GE -1`:** the stable public ABI value remains `2` (`NEC_GROUND_CONNECTION_ZERO_CURRENT`), while the native geometry receives `-1`. Previously `GE -1` was documented but effectively treated as no ground: `build_connections()` guarded every ground check with `ignd > 0`, so zero-current geometries skipped the plane checks the manual mandates. Both signed ground modes now reject segments that extend below the ground plane or lie in it (a segment may still end on the plane), and a non-none connection without a ground model (`GN` card) fails at `simulate()` instead of silently running free space — NEC-2 Part 3: "A positive or negative value of I1 does not cause a ground to be included in the calculation... The ground parameters must be specified on a program control card following the geometry cards." The `GE -1` connection semantics are unchanged from the Fortran: a ground-touching end stays a free end, so the current goes to zero there, and the low-horizontal-wire escape hatch (height < 1e-3 × segment length) still applies. `testharness/data/discone.nec` gained the missing `GN 1`; `test_example1` now completes the geometry with 0, matching its free-space deck.
 * **`nec2diff` no longer reports spurious radiation-pattern differences:** at angles where the polarization is undefined (HORIZ gain `-999.99`, e.g. at the horizon) NEC leaves the SENSE column blank. The `RadiationInput` parser read the next numeric token as the sense string, shifting the remaining columns left by one, and `read_fixed`/`read_sci` returned **uninitialized memory** when the stream was exhausted — so comparing a file against itself reported a nonzero difference with garbage values (observed on `bruce_sommerfeld`). The parser now detects the blank SENSE column, and the readers return 0.0 on extraction failure. All 52 testharness decks now self-compare exactly clean; genuine differences are still flagged.
+* **`gshank` Shanks-tail convergence floor restored after it caused non-terminating Sommerfeld integrations:** issue #131 item 3 also raised gshank()'s convergence floor from `denm = 1e-3*den*CRIT` to `2e-1*den*CRIT_H` — 200× looser. On decks with wires close to a `GN 2` ground (e.g. a radial screen elevated 0.2 m over epsr 13 / sig 0.005 at 2.7 MHz), the truncated Shanks tail degrades the Sommerfeld tables enough that `rom2()` can never meet its `RX = 1e-4` Romberg test: the integration doubles to the 65536-subdivision cap at every step, emits an endless `ROM2 -- STEP SIZE LIMITED` stream (GB/minute into both stdout and the output file) and effectively never terminates. The same deck completes in ~14 ms with the previous floor, agreeing with `nec2c` (13.906 − j445.84 Ω). The floor is restored to `1e-3*den*CRIT_H` while the milder `CRIT_H = 1.1e-4` tail-test scaling is kept; output is byte-identical (modulo timing lines) to the pre-loosening build on `sommerfeld2/3` and `bruce_sommerfeld`. Regression decks: `testharness/data/wire_order_normal.nec`, `wire_order_reversed.nec`; unit test `[issue139]` (which also fails on this regression via timeout).
+* **`nec2diff` compares negative values, reports finite sign-flip differences, and exits non-zero when results differ (#138):** the real-valued `diff()` in `BaseInput.h` tested *signed* values against the near-zero floor (`a < 1e-8 && b < 1e-8`), so any two negative numbers compared equal — a 178 Ω negative-reactance change (`−179.39 → −1.00`) or a `−1.71 → −9.71 dBi` gain change reported `Difference = 0`. A pure sign flip (`−179.39 → +179.39`) divided by `|a+b| = 0` and printed `inf`. Both `diff()` overloads now normalize by the larger magnitude (`|a−b|/max(|a|,|b|)`), keeping the near-zero early-out but keyed on absolute values. Two behavioral notes: (1) this metric is close to twice the old `|a−b|/|a+b|` for near-equal values, so the `equalto()` thresholds (sum ≤ 1e-4) now bind about twice as tightly and previously hidden last-digit engine discrepancies are visible in `nec2diff` output; (2) `main()` now tracks a flag across the three sections and returns 1 if any section differs, so scripts and harnesses can rely on the exit status. `nec2diff` with fewer than two arguments prints usage and returns 1 instead of throwing `std::logic_error` from a null `std::string` construction. Regression fixtures and an exit-code test live in `tests/data/issue138/` (ctest `necpp_nec2diff_issue138`); the four cases report 0.994, 0.824, 0.167 (control) and a finite 2.0, matching the reporter's values.
 
 ### Performance
 * **`saoa` shares one `xl*xl` across all five uses:** the Sommerfeld integrand squared `xl` independently for each of `cgam1`, `cgam2` (the two complex `sqrt` arguments), the three `dgam` large-|xl| branches, and the `rho==0` transverse answer. One complex multiply per integrand evaluation is now shared (issue #131). Algebraic identity — byte-identical output on all five `GN 2` decks; benchmarked at ≤0.1% on a noisy laptop, consistent with the multiplication being a small fraction of the transcendental-dominant kernel.