Re: Re: Interaction of Sum/Plus and KroneckerDelta

*To*: mathgroup at smc.vnet.net*Subject*: [mg55291] Re: [mg55259] Re: Interaction of Sum/Plus and KroneckerDelta*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 18 Mar 2005 05:34:20 -0500 (EST)*References*: <d192un$ngm$1@smc.vnet.net> <200503170831.DAA21883@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 17 Mar 2005, at 09:31, Paul Abbott wrote: > Again, without a definite value for j, this is the correct answer. It > should _not_ be transformed to one. Why? Because if you multiply this > expression by a function depending on the parameter j, say > > (KroneckerDelta[1, j] + KroneckerDelta[2, j]) f[j] > > then which one of KroneckerDelta[1, j] and KroneckerDelta[2, j] > evaluates to 1 effects the result. > Hmm... Let's see KD[i_, j_] := Piecewise[{{1, i == j}}] Simplify[(KD[1,j]+KD[2,j])*f[j],j==1||j==2] f(j) ;-) Andrzej

**References**:**Re: Interaction of Sum/Plus and KroneckerDelta***From:*Paul Abbott <paul@physics.uwa.edu.au>