- changed function::diff() to be more tolerant by checking first if the

[ginac.git] / ginac / diff.cpp

diff --git a/ginac/diff.cpp b/ginac/diff.cpp
index 7b4d489b76b6dc1a51e572c9326657282411f5d7..2661fddb849bbab612c2aabf1a0bfec25d5c1333 100644 (file)
--- a/ginac/diff.cpp
+++ b/ginac/diff.cpp
@@ -175,17 +175,22 @@ ex power::diff(symbol const & s) const
 ex function::diff(symbol const & s) const
 {
     exvector new_seq;
 ex function::diff(symbol const & s) const
 {
     exvector new_seq;

-
-    if (serial == function_index_Order) {
-
+    
+    if (serial==function_index_Order) {

         // Order Term function only differentiates the argument
         return Order(seq[0].diff(s));
         // Order Term function only differentiates the argument
         return Order(seq[0].diff(s));

-

     } else {
     } else {

-

         // Chain rule
         // Chain rule

+        ex arg_diff;

         for (unsigned i=0; i!=seq.size(); i++) {
         for (unsigned i=0; i!=seq.size(); i++) {

-            new_seq.push_back(mul(pdiff(i), seq[i].diff(s)));
+            arg_diff = seq[i].diff(s);
+            // We apply the chain rule only when it makes sense.  This is not
+            // just for performance reasons but also to allow functions to
+            // throw when differentiated with respect to one of its arguments
+            // without running into trouble with our automatic full
+            // differentiation:
+            if (!arg_diff.is_zero())
+                new_seq.push_back(mul(pdiff(i), arg_diff));

         }
     }
     return add(new_seq);
         }
     }
     return add(new_seq);