       Re: How to substitute?

• To: mathgroup at smc.vnet.net
• Subject: [mg45543] Re: How to substitute?
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Tue, 13 Jan 2004 04:03:57 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <btndpp\$4f\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

\!\(\((y\_0 - z\_3)\)\ \((\(-y\_1\) + z\_3)\)\ \((\(-y\_2\) +
z\_3)\)\ \((\(-y\_3\) + z\_3)\)\  /. \ \((a_. *y\_i_ +
b_. \ \ z\_j_)\) :> \ Q[{a, i}, {b, j}]\)

Regards
Jens

Steve Gray 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-z) (y-z) (y - z), 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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