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Why symsum does not provide the right result?

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Serbring
Serbring 2021-5-18
评论： Serbring 2021-5-18
Hi all,
I need to find the symbolic solution of the sum of the mathematical series, but symsum does not provide the right result. Here you an example with the serie: .
syms i
symsum(i,i)
ans =
i^2/2 - i/2
This is very different from the theretical result. However, if I limit the series as follows:
symsum(i,i,0,100)
ans =
5050
That is corect. However, it is differente than
subs(symsum(i,i),i,100)
ans =
4950
Why symsum does not provide the right result?

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采纳的回答

Jan
Jan 2021-5-18
Ran in:
syms i n
symsum(i,i, 1, n)
ans = 
If you define the sum without limits like in symsum(i,i) something different is calculated according to the documentation ( doc symsum ):
F = symsum(f,k) returns the indefinite sum (antidifference) of the series f with respect to the summation index k. The f argument defines the series such that the indefinite sum F satisfies the relation F(k+1) - F(k) = f(k).

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