Re: How to substitute?

• To: mathgroup at smc.vnet.net
• Subject: [mg45498] Re: How to substitute?
• From: bobhanlon at aol.com (Bob Hanlon)
• Date: Sat, 10 Jan 2004 00:00:48 -0500 (EST)
• References: <btndpp\$4f\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```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 smc.vnet.net>, Steve Gray <stevebg at adelphia.net> 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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