How can I make a sigma sum graph?

For example there are following graph for "x" and "q".

fun = @(x) x;

pb = 1:500;

a1 = length(pb);

q = zeros(1,a1);

for a = 1:a1

q(a) = -integral(fun,500,pb(a));

end

I want to replace the integral to a sigma sum for some steps.

I'd like to use a way of adding values as pb is closer to zero.

How can I do?

[Akira Agata]

You mean, you would like to calculate the following equation for x = 1 ~ 500, and plot the result ?

Answer 1

[Jyotsna Talluri]

Hi,

As the integral and summation are two different functions,we can't get the exact same results with the both.As the lower limit of integration is closer to zero both produce comparable results that don't differ much.For sigma sum you can use symsum function.

https://www.mathworks.com/help/symbolic/symsum.html

syms x;
f=x;
q(a)=symsum(f,x,pb(a),500);