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MathGroup Archive 2005

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Interesting failure of Collect

  • To: mathgroup at
  • Subject: [mg61307] Interesting failure of Collect
  • From: "Blimbaum, Jerry CIV NSWC PC" <jerry.blimbaum at>
  • Date: Fri, 14 Oct 2005 22:22:38 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Given the expr =  Sin[p]/(4 Pi a) + Sin[p]/(4 Pi b)  

and then applying the command

Collect[expr, Sin[p]/(4 Pi)] works as it should, however,

expr2 = Sin[p]/(4 Pi a) - Sin[p]/(4 Pi b)  

leaves the expression untouched.   (I realize I could use Simplify but
this problem occurred on a much longer expression and this is intended
just to convey the basic idea)....for longer expressions the Collect
process works for all quantities with a + sign but the one with a minus
sign will not be collected.....strikes me as a "bug".....

thanks....jerry blimbaum

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