[WWcvs] pg: Fix substitute() so that if the variable is being substituted for a constant, only the branch that contains that value is

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

Log Message:
-----------
Fix substitute() so that if the variable is being substituted for a
constant, only the branch that contains that value is returned.  If it
is substituted by another variable, the variables for the inequalities
will also be changed.  (Otherwise the variable is replaced only in the
functions; not perfect, but the best that I could come up with.)

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

Revision Data
-------------
Index: contextPiecewiseFunction.pl
===================================================================
RCS file: /webwork/cvs/system/pg/macros/contextPiecewiseFunction.pl,v
retrieving revision 1.1
retrieving revision 1.2
diff -Lmacros/contextPiecewiseFunction.pl -Lmacros/contextPiecewiseFunction.pl -u -r1.1 -r1.2
--- macros/contextPiecewiseFunction.pl
+++ macros/contextPiecewiseFunction.pl
@@ -513,16 +513,29 @@
 
 #
 #  Substitute into each branch individually.
-#
-#  ### FIXME: only allow the variable to be substituted
-#    by another variable, and change the intervals as well.
-#    If it is a constant, then evaluate?
+#  If the function's variable is substituted, then
+#    if it is a constant, find the branch for that value
+#    and substitute into that, otherwise if it is
+#    just another variable, replace the variable
+#    in the inequalities as well as the formulas.
+#  Otherwise, just replace in the formulas.
 #
 sub substitute {
-  my $self = shift; my @cases = ();
+  my $self = shift;
+  my @cases = (); my $x = $self->{varName};
+  $self->setValues(@_); my $a = $self->{values}{$x}; $self->unsetValues(@_);
+  if (defined $a) {
+    if (!Value::isFormula($a)) {
+      my $f = $self->getFunctionFor($a);
+      die "undefined value" unless defined $f;
+      return $f->substitute(@_);
+    }
+    $x = $a->{tree}{name} if $a->{tree}->class eq 'Variable';
+  }
   foreach my $If (@{$self->{data}}) {
     my ($I,$f) = @{$If};
-    push(@cases,$I->copy => $f->substitute(@_));
+    $I = $I->copy; if ($x ne $I->{varName}) {$I->{varName} = $x; $I->updateParts}
+    push(@cases,$I => $f->substitute(@_));
   }
   push(@cases,$self->{otherwise}->substitute(@_)) if defined $self->{otherwise};
   return $self->make(@cases);
@@ -580,6 +593,41 @@
 }
 
 #
+#  Look up the function for the nth branch (or the "otherwise"
+#  function if n is omitted or too big or too small).
+#
+sub getFunction {
+  my $self = shift; my $n = shift;
+  return $self->{otherwise} if !defined $n || $n < 1 || $n > $self->length;
+  return $self->{data}[$n-1][1];
+}
+
+#
+#  Look up the domain for the nth branch (or the "otherwise"
+#  domain if n is omitted or too big or too small).
+#
+sub getDomain {
+  my $self = shift; my $n = shift;
+  return $self->Package("Inequality")->new($self->context,
+    $self->domainR - $self->domainUnion,$self->{varName})
+       if !defined $n || $n < 1 || $n > $self->length;
+  return $self->{data}[$n-1][0];
+}
+
+#
+#  Get the function for the given value of the variable
+#  (or undef if there is none).
+#
+sub getFunctionFor {
+  my $self = shift; my $x = shift;
+  foreach my $If (@{$self->{data}}) {
+    my ($I,$f) = @$If;
+    return $f if $I->contains($x);
+  }
+  return $self->{otherwise};
+}
+
+#
 #  Implements the <=> operator (really only handles equality ir not)
 #
 sub compare {