Re: Condition in replacement rule
- To: mathgroup at smc.vnet.net
- Subject: [mg67781] Re: Condition in replacement rule
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Fri, 7 Jul 2006 07:13:07 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 7/6/06 at 6:52 AM, wandering.the.cosmos at gmail.com wrote:
>I have a replacement rule that goes like
>A[V,W_] -> A[V,W] + B[W]
>but I want to perform this replacement if and only if V and W are
>not the same. It seems
>A[V,W_/;W!=V] -> A[V,W] + B[W]
>does not seem to work. How should I do this?
Using RuleDelayed the following should work
A[V_,W_]:>If[W != V, A[V,W]+B[W], A[V,W]]
Checking to confirm
In[2]:=
A[1, 2] /. A[V_, W_] :> If[W != V, A[V, W] + B[W],
A[V, W]]
Out[2]=
A[1, 2] + B[2]
In[3]:=
A[1, 1] /. A[V_, W_] :> If[W != V, A[V, W] + B[W],
A[V, W]]
Out[3]=
A[1, 1]
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