[WWcvs] pg: Added differentiation of (single-variable) functions created with

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
Added differentiation of (single-variable) functions created with
parserFunction.

Modified Files:
--------------
    pg/macros:
        parserFunction.pl

Revision Data
-------------
Index: parserFunction.pl
===================================================================
RCS file: /webwork/cvs/system/pg/macros/parserFunction.pl,v
retrieving revision 1.1
retrieving revision 1.2
diff -Lmacros/parserFunction.pl -Lmacros/parserFunction.pl -u -r1.1 -r1.2
--- macros/parserFunction.pl
+++ macros/parserFunction.pl
@@ -78,7 +78,7 @@
       @_, class => 'parserFunction', argCount => scalar(@argNames),
       argNames => [@argNames], argTypes => [@argTypes],
       function => $formula->perlFunction(undef,[@argNames]),
-      type => $formula->typeRef,
+      formula => $formula, type => $formula->typeRef,
     }
   );
   main::PG_restricted_eval("sub main::$name {Parser::Function->call('$name',\@_)}");
@@ -120,6 +120,20 @@
 }
 
 #
+#  Compute the derivative of (single-variable) functions
+#    using the chain rule.
+#
+sub D {
+  my $self = shift; my $def = $self->{def};
+  $self->Error("Can't differentiate function '%s'",$self->{name})
+    unless $def->{argCount} == 1;
+  my $x = $def->{argNames}[0];
+  my $Df = $def->{formula}->D($x);
+  my $g = $self->{params}[0];
+  return (($Df->substitute($x=>$g))*($g->D(@_)))->{tree}->reduce;
+}
+
+#
 #  Get the name for a number
 #
 sub NameForNumber {