       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

```

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