From d269bd380509ef1782d4a5af12172ea801640b50 Mon Sep 17 00:00:00 2001
From: h_vogt <h_vogt>
Date: Sun, 9 Jun 2013 11:06:05 +0200
Subject: [PATCH] nicomcof.c: xmu used to calculate trap integration
 coefficient

---
 src/maths/ni/nicomcof.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/maths/ni/nicomcof.c b/src/maths/ni/nicomcof.c
index 7dcd7ed38..2dfb8f64b 100644
--- a/src/maths/ni/nicomcof.c
+++ b/src/maths/ni/nicomcof.c
@@ -7,6 +7,11 @@ Author: 1985 Thomas L. Quarles
 #include "ngspice/cktdefs.h"
 #include "ngspice/sperror.h"
 
+/* xmu=0: Backward Euler, xmu=0.5: trapezoidal (standard),
+   xmu=0.48: good damping of current ringing, e.g. in R.O.s.
+   SpiceOpus adapts xmu to lower values if numerical oscillations
+   of current in capacitors are detected, t.b.d. */
+#define xmu 0.5
 
 int
 NIcomCof(CKTcircuit *ckt)
@@ -17,6 +22,7 @@ NIcomCof(CKTcircuit *ckt)
     double arg;
     double arg1;
 
+
     /*  this routine calculates the timestep-dependent terms used in the
      *  numerical integration.
      */ 
@@ -35,10 +41,8 @@ NIcomCof(CKTcircuit *ckt)
             break;
 
         case 2:
-            ckt->CKTag[0]=1.0/ckt->CKTdelta/(1.0-0.5) ;
-            ckt->CKTag[1]=0.5/(1.0 - 0.5) ;
-            /* above lines should have 'xmu' instead of .5 eventually */
-            /* (in all three places) */
+            ckt->CKTag[0] = 1.0 / ckt->CKTdelta/(1.0 - xmu) ;
+            ckt->CKTag[1] = xmu / (1.0 - xmu) ;
             break;
 
         default: