# Does Matlab's integral function pass the integration variable to the function handle one scalar at a time or as a vector?

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yuval dahan on 24 Jun 2024
Commented: yuval dahan on 24 Jun 2024
Hello,
My integrand function contains a sum that depends on the integration variable, as follows:
tau = 1;
T = 20;
q = integral(@(t) f(t,tau),0,T)
function y = f(t,tau)
N = 0:floor(t,tau)
for i = 1:length(N)
n = N(i);
y = y + g(n,mod(t,tau) + (n+1)*tau) - g(n,mod(t,tau) + n*tau);
end
Where g is some function.
I'm not sure if the integral function is handling it correctly, because if it passes a vector t, the sum will not iterate over the correct range.
I would really appreciate any insights!
Thanks!

Stephen23 on 24 Jun 2024
Edited: Stephen23 on 24 Jun 2024
"Does Matlab's integral function pass the integration variable to the function handle one scalar at a time or as a vector?"
By default it assumes that the function is vectorized, i.e. accepts a vector and returns a vector of the same size. This is explained in the documentation: "for scalar-valued problems, the function y = fun(x) must accept a vector argument, x, and return a vector result, y."
If your function only accepts a scalar, then set the 'ArrayValued' option to true:
q = integral(@(t) f(t,tau), 0,T, 'ArrayValued',true)
##### 3 CommentsShow 1 older commentHide 1 older comment
John D'Errico on 24 Jun 2024
All that has been said is true. HOWEVER, I would add a caveat. If you are having problems with the integral, then there is some potential the problem lies in your function g, and in what you do. The use of mod makes your function highly non-smooth.
As such, I would strongly recommend you plot the function you are trying to integrate here. I would do so, but you don't supply g, so we cannot help you more.
yuval dahan on 24 Jun 2024
Thank you both! It was very helpfull

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