I do not know how to work with regress() but applying a function to a section of a vector/matrix usually works like this:
x = rand(1, 1000);
y = rand(1, 1000);
for i = 1:100:1000
anyFunction(x(i:i+99), y(i:i+99))
end
There are numerous ways to achive this, though, but this is a good way to begin with.
