[WWcvs] pg: Derivatives of absolute values were leaving out the chain rule when written as |...| (but not as abs(...)).

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

Log Message:
-----------
Derivatives of absolute values were leaving out the chain rule when
written as |...| (but not as abs(...)).  The chain rule is built into
the derivatives of function objects automatically, but not of lists,
which is how |...| is implemented (a special form of parentheses), and
so I missed it when adding the derivative in this form.  Argh!

Modified Files:
--------------
    pg/lib/Parser:
        Differentiation.pm

Revision Data
-------------
Index: Differentiation.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Parser/Differentiation.pm,v
retrieving revision 1.12
retrieving revision 1.13
diff -Llib/Parser/Differentiation.pm -Llib/Parser/Differentiation.pm -u -r1.12 -r1.13
--- lib/Parser/Differentiation.pm
+++ lib/Parser/Differentiation.pm
@@ -602,7 +602,12 @@
 sub Parser::List::AbsoluteValue::D {
   my $self = shift; my $x = $self->{coords}[0]->copy;
   my $equation = $self->{equation};
-  return $self->Item("BOP")->new($equation,'/', $x, $self->copy);
+  my $BOP = $self->Item("BOP");
+  return
+    $BOP->new($equation,"*",
+      $BOP->new($equation,'/', $x, $self->copy),
+      $x->D(shift),
+   );
 }