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Specify TransformationFunctions in Simplify[] gives wrong result

  • To: mathgroup at
  • Subject: [mg125865] Specify TransformationFunctions in Simplify[] gives wrong result
  • From: Yi Wang <tririverwangyi at>
  • Date: Thu, 5 Apr 2012 05:52:21 -0400 (EDT)
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Hi, all,

I met a problem when using the TransformationFunctions option in Simplify:

PDD[a_?NumericQ, idx_] := 0;
t = aa PDD[z, d];
try[expr_] := Replace[expr, aa_. PDD[bb_, cc_] :> -bb PDD[aa, cc]];
Simplify[t, TransformationFunctions :> {try}]

I expect Simplify to do nothing, because the replace rule in try[] does not make the function simpler in this special case. However, Simplify[...] returns 0.

If I delete the line " PDD[a_?NumericQ, idx_] := 0; ", Simplify will give the correct result. However, z (or N[z]) is not a number thus it seems the above line shouldn't matter.

I also tried several other tests. I found a_?NumberQ, a_?IntegerQ both have the above problem, while a_ListQ has the desired behaviour.

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