Replacing an expression by an expression

• To: mathgroup at smc.vnet.net
• Subject: [mg55625] Replacing an expression by an expression
• Date: Thu, 31 Mar 2005 01:24:56 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```I have a 8 x 8 symbolic matrix B of complicated entries.
Several partial expressions, however, can be simplified. Sample:

rep= {(J12*x14-J11*y14)*(J12*(x32+x43)-J11*(y32+y43)) -> A0*(A1-A0)};

The left expression appears verbatim in entry B[[1,1]], which is

-(L21*(J12*x14-J11*y14)*(J12*(-x32-x43)+J11*(y32+y43)))/
(16*A412*J*(J11^2+J12^2))

But when I say B=B/.rep, nothing happens.  For a few entries I could do
cut and paste by hand:

-(L21*  A0*(A1-A0)    )/
(16*A412*J*(J11^2+J12^2))

But it get tedious and error prone for 64.  Any suggestions on how to
get Mathematica to do the replacement?

```

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