This IS your preallocation of G. After executing this line, G is at its final size. You never add nor remove an element in your for loop.
for i=1:size(G);
if -h_s(i) < T < h_s(i);
This doesn't do what you think it does. This is equivalent to the following, with the variable name shortened to make it a bit shorter.
I'll show four examples of why this doesn't work the way you think it does.
Let T = 1, h = 2. T is between -h and h so you expect this to return true. -2 < 1 is true and true < 2 is true so it does return true.
Let T = -0.5, h = 0.75. T is between -h and h so you expect this to return true. -0.75 < -0.5 is true and true < 0.75 is false so it returns false.
Let T = 2, h = 1.5. T is not between -h and h so you expect this to return false. -1.5 < 2 is true and true < 1.5 is true so it returns true.
Let T = 2, h = 0.5. T is not between -h and h so you expect this to return false. -0.5 < 2 is true and true < 0.5 is false so it returns false.
Instead use (-h < T) & (T < h).
G(i)=Bic(i)+dif(i)+Ri(i);
else
G(i)=0;
end
end
You can vectorize the computation using linear indexing. You've already computed the first part of your if statement, so all you need to do is reject those elements that are "out of bounds".
G=Bic+dif+Ri;
listOfNonDay = (-h < T) & (T < h);
G(listOfNonDay) = 0;
