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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>
*Reply-to*: kuska at informatik.uni-leipzig.de
*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[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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