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Re: Re: Interaction of Sum/Plus and KroneckerDelta


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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