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MathGroup Archive 2007

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Replacements in NonCommutativeMultiply

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72558] Replacements in NonCommutativeMultiply
  • From: "David Park" <djmp at earthlink.net>
  • Date: Mon, 8 Jan 2007 05:00:36 -0500 (EST)

Can anyone explain the following result?

Times[a, NonCommutativeMultiply[], NonCommutativeMultiply[i, c]];
% /. NonCommutativeMultiply[] -> 1 // FullForm

giving

Times[a, NonCommutativeMultiply[1, i, c]]

I believe the result should be

Times[a, NonCommutativeMultiply[i, c]]

The reason I get an empty argument sequence is that the factors contain 'scalars' and 'vectors' and the scalars get factored out. Only the vector part is noncommutative.

The result Mathematica gives is definitely a problem because when the 1 is factored out again to simplify we arrive back at the starting point.

A similar replacement is done with CircleDot works properly.

Times[a, CircleDot[], CircleDot[i, c]];
% /. CircleDot[] -> 1 // FullForm

Times[a, CircleDot[i, c]]

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 



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