# How do I simplify this symbolic summation?

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Nélio Dias 2022 年 10 月 15 日

Hello, I have this operation
syms e(k) T_s k
e(k) = symsum(e*T_s,k,[0 k])
Warning: Summation variable must not occur on the right side.
e(k) =
result = e(k)-e(k-1)
Warning: Summation variable must not occur on the right side.
Warning: Summation variable must not occur on the right side.
result =
So with k integer, the result have to be
So there is a way to simplify the result in matlab or to set this result in the code?
Thanks

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### 回答 (1 件)

Torsten 2022 年 10 月 15 日
syms e(k) T_s n
e(n) = symsum(T_s*e(k),k,[0 n])
e(n) =
result = simplify(e(n)-e(n-1)) % doesn't simplify
result =
result = simplify(e(20)-e(19)) % simplifies
result =
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Nélio Dias 2022 年 10 月 15 日
But have to be
Because I have
So the result have to be
Torsten 2022 年 10 月 15 日

Internally, the result will be correct, but MATLAB doesn't simplify to this simple expression.
And don't use the same variable for upper limit and loop index - it doesn't make sense and MATLAB dislikes it as you could see from the warnings for your first attempt.

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