for i = 1:7
for j = 1:7
P(i,j) = factorial(i + j - 2)./(2*factorial(j - 1));
for a 4x4 matrix, change the 7 in lines 1 and 2 to 4! But with this formulation, I wonder how it can be symmetric. I'm guessing you've mistyped the question and the denominator has to be (i-1)!(j-1)! which will set things correct!
and hence the line 3 in the code above will be:
P(i,j) = factorial(i + j - 2)./(factorial(j - 1)*factorial(i - 1));
Oh, and BTW, MATLAB (as usual), has a function called pascal, and you need to just say pascal(4) or pascal(7)!