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Re: Simplifying with KroneckerDelta

  • To: mathgroup at smc.vnet.net
  • Subject: [mg101447] Re: [mg101426] Simplifying with KroneckerDelta
  • From: "David Park" <djmpark at comcast.net>
  • Date: Tue, 7 Jul 2009 07:50:35 -0400 (EDT)
  • References: <1551538.1246958483039.JavaMail.root@n11>

Why not use a rule?

krule = b_ KroneckerDelta[a_, b_] -> a KroneckerDelta[a, b]

(m + n) KroneckerDelta[k, m + n] /. Krule
k KroneckerDelta[k, m + n]

But the real work might be if you have a sum before the KroneckerDelta that
only includes m + n as sub-terms. You could write a routine that collected
on the KroneckerDelta forms, then wrapped Hold around the m+n sub-terms
(both places), then applied the rule and released the Hold.


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: frojasf [mailto:fjrojas at gmail.com] 


Hello,

Does anybody know how to tell mathematica to use the KroneckerDelta in order
to simplify expressions? For example, it would be great if it could receive
something like this:

(m+n) KroneckerDelta[k,m+n]  and give

k KroneckerDelta[k,m+n]

Of course this is simple example, but I have an expression which is about
200 terms long, so if it could use the delta to simplify things by itself,
that would be great.

Thanks to all in advance,
Francisco
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