Why symsum does not provide the right result?

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?

Answer 1

[Jan]

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).

[Serbring]

It worked. thank you so much.