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Re: How to substitute?

  • To: mathgroup at
  • Subject: [mg45498] Re: How to substitute?
  • From: bobhanlon at (Bob Hanlon)
  • Date: Sat, 10 Jan 2004 00:00:48 -0500 (EST)
  • References: <btndpp$4f$>
  • Sender: owner-wri-mathgroup at

Your examples appear inconsistent (y-z or z-y?).  However, you should be able
to modify the following for whatever your intended output.

expr /. a_.* Subscript[y,i_] + b_.* Subscript[z,j_] :> Subscript[Q, a*i, b*j]

expr /. a_. * y[i_] + b_. * z[j_] :> Q[a*i, b*j]

Bob Hanlon

In article <btndpp$4f$1 at>, Steve Gray <stevebg at> wrote:

\!\(\((y\_0 - z\_3)\)\ \((\(-y\_1\) + z\_3)\)\ \((\(-y\_2\) + 
        z\_3)\)\ \((\(-y\_3\) + z\_3)\)\)

	I have output cells containing various expressions such as 
(y[0]-z[1]) (y[1]-z[2]) (y[4] - z[0]), where I use [x] here to mean
subscript. The integers can have any small values. For compactness of
expression, I want to make substitutions which make the above
expression look like Q[0,1]Q[1,2]Q[4,0]. There are many combinations
of subscript pairs and I don't want to write explicit substitution
rules for every possible combination. I tried doing /.(y[i]-z[j]) ->
Q[i,j] , and /.(y[i_]-z[j_]) -> Q[i,j] but they don't work. 
	Any suggestions will be gratefully received.

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