How do I simplify this symbolic summation?

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

Answer 1

[Torsten]

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 = 

[Nélio Dias]

But have to be

Because I have

So the result have to be

[Torsten]

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.