How can I complete summation of variable named matrices in loop?

If matrices are variable (1:N) with names s_1:s_N how can I complete summation of the matrices. Below is my current script which errors out for matrix dimensions do not agree. I understand this error and I understand I cannot call matrices using ['s_', num2str(i)] but still not sure how to move forward with summation.

%% s_1, s_2, s_3, s_4 are all known matrices with values 3500x4 double. Matrices will vary - created 4 just for debugging.

N = 4

sumCST1 = zeros(size(s_1));

for i = 2:N      

    sumCST1 = sumCST1 + ['s_', num2str(i)] 

end

Error using + Matrix dimensions must agree.

Answer 1

[Branden Chamness]

figured it out from another thread:

sumCST1 = zeros(size(s_1));

for i = 1:N      

    s = ['s_' num2str(i)];
    sumCST1 = sumCST1 + eval(s)

end