You need to save the values from each iteration in an array. Check this code
Gmodulus = 1; % example values
Emodulus = 2;
x = 0:0.01:1;
CompMod = zeros(size(x));
for i = 1:numel(x)
CompMod(i) = (Gmodulus*x(i))+(Emodulus*(1-x(i)));
end
plot(x,CompMod)
