Conversion to cell from double is not possible.

n = input("enter the basis matrix dimension:  ");
alpha2 = ones(1,n)*sqrt(2/n);
alpha2(1) = sqrt(1/n);
alpha1 = ones(1,n)*sqrt(2/n);
alpha(1) = sqrt(1/n);
for u = 0:n-1
    for v = 0:n-1
        for x = 0:n-1
            for y = 0:n-1
                a {u+1,v+1}(x+1,y+1) = alpha1(u+1)*alpha2(v+1)*...
                    cos((2*x+1)*pi*u/(2*n))*cos((2*y+1)*pi*v/(2*n));
            end
        end
    end
end