Matrix loop

[Riccardo Corradini]

Hi,
I would know if is there a more efficient way to perform the following operation
s_cR =21;
n=1000;
a= rand(s_cR,s_cR,n);
whos a
meant = mean(a,3);
whos meant
for tt=1:n
    b(:,:,tt) = a(:,:,tt) - meant;
    c(:,:,tt)= b(:,:,tt) * b(:,:,tt)';
endfor
result = sum(c,3)*1/n;
whos result

Thanks in advance