From 7be4dc785e686180733ba295b308cb83d0c1a9d0 Mon Sep 17 00:00:00 2001
From: h_vogt <h_vogt>
Date: Sun, 9 May 2010 18:57:31 +0000
Subject: [PATCH] derivatives for min, max

---
 ChangeLog                      |  1 +
 src/spicelib/parser/inpptree.c | 47 ++++++++++++++++++++++++++--------
 2 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 8d1eb2add..278758470 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,7 @@
 2010-05-09 Holger Vogt
  * inpcom.c: patch 09/05/10 by Robert
  * spinit.in: add ngbehavior
+ * inpptree.c: derivatives for fcns min and max
 
 2010-05-08 Holger Vogt
  * inpcom.c: patch 02/05/10 by Robert: avoid subtraction from a builtin 1.0
diff --git a/src/spicelib/parser/inpptree.c b/src/spicelib/parser/inpptree.c
index c27e8a4ae..bd34b8f2f 100644
--- a/src/spicelib/parser/inpptree.c
+++ b/src/spicelib/parser/inpptree.c
@@ -2,7 +2,7 @@
 Copyright 1990 Regents of the University of California.  All rights reserved.
 Author: 1987 Wayne A. Christopher, U. C. Berkeley CAD Group 
 **********/
-/*#define TRACE*/
+//#define TRACE
 
 #include "ngspice.h"
 #include "ifsim.h"
@@ -441,17 +441,42 @@ static INPparseNode *PTdifferentiate(INPparseNode * p, int varnum)
             arg1 = mkcon((double) 0.0);
             break;
 
-        case PTF_MIN:
-        /*
-        min(a,b)
-        p->left: ','    p->left->left: a       p->left->right: b 
-        */	        
-            newp = mkcon((double) 0);
-	        return (newp);
+    case PTF_MIN:
+    case PTF_MAX:
+        /* min(a,b) -->   (a<b)       ? a : b
+        *           -->   ((a-b) < 0) ? a : b
+        */
+        {
+            INPparseNode *a = p->left->left;
+            INPparseNode *b = p->left->right;
+            int comparison = (p->funcnum == PTF_MIN) ? PTF_LT0 : PTF_GT0;
+#ifdef TRACE
+            extern void printTree(INPparseNode *);
 
-        case PTF_MAX:
-            newp = mkcon((double) 0);
-	        return (newp);
+            printf("debug: %s, PTF_MIN: ", __func__);
+            printTree(p);
+            printf("\n");
+            printf("debug: %s, PTF_MIN, a: ", __func__);
+            printTree(a);
+            printf("\n");
+            printf("debug: %s, PTF_MIN, b: ", __func__);
+            printTree(b);
+            printf("\n");
+#endif
+            newp = mkb(PT_TERN,
+                       mkf(comparison, mkb(PT_MINUS, a, b)),
+                       mkb(PT_COMMA,
+                           PTdifferentiate(a, varnum),
+                           PTdifferentiate(b, varnum)));
+#ifdef TRACE
+            printf("debug, %s, returns; ", __func__);
+            printTree(newp);
+            printf("\n");
+#endif
+            return (newp);
+        }
+
+        break;
 
         case PTF_POW:
         {