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MathGroup Archive 1992

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Re: Dot[]->1

  • To: mathgroup at
  • Subject: Re: Dot[]->1
  • From: a_rubin at (arthur rubin)
  • Date: Fri, 7 Aug 92 07:36:35 PDT

trott at (Trott Michael) writes:

 Hi mathgroup,

 On simplifying some large expressions via some rules I ended with
 expressions of the following type:

 Dot[]+Dot[x,y] .
 In this expression I would like to replace the first part by 1. So I tried:

 (Dot[] + Dot[x,y])/.{Dot[]->1}.

 But the result was not what I expected (1+x.y), but rather

 1 + 1.x.y   .
 Can somebody tell me how to do my disired replacement and what happens
 in the described example?
Dot has the attribute "Flat", so that Dot[].x = x; I think the best way to
fix it would be to use:

X_Dot :> If[Length[X]===0,1,X]

Not elegant, but it works.

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