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RE: How to substitute?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg45489] RE: [mg45474] How to substitute?
*From*: "David Park" <djmp at earthlink.net>
*Date*: Sat, 10 Jan 2004 00:00:36 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
Steve,
expr = (Subscript[y, 0] - Subscript[z, 3])*
(-Subscript[y, 1] + Subscript[z, 3])*
(-Subscript[y, 2] + Subscript[z, 3])*
(-Subscript[y, 3] + Subscript[z, 3])
expr //. {Subscript[y, i_] - Subscript[z, j_] ->
Q[i, j], -Subscript[y, i_] + Subscript[z, j_] ->
-Q[i, j]}
-Q[0, 3] Q[1, 3] Q[2, 3] Q[3, 3]
(I used Bobby Treat's neat copy palette to copy and paste these
expressions.)
David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/
From: Steve Gray [mailto:stevebg at adelphia.net]
To: mathgroup at smc.vnet.net
\!\(\((y\_0 - z\_3)\)\ \((\(-y\_1\) + 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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