Series representation of Vibrations of a membrane

I am having trouble getting my matlab code to properly calculate and then graph a series representation of a vibrating membrane. I have the equation, but I am concerned that my code is not correct. Can you see any obvious errors?

The equation is:

u(x,y,t)=(16/pi^2)*sum(n odd)sum(m odd) (1/(n*m*sqrt(n^2+m^2))*sin(m*pi*x)*sin(n*pi*y)*sin(t*sqrt(m^2+n^2)

The function I wrote to implement the series sum is:

function [ z ] = solHwFeb29375b( x,y,t )

f=0;

   for m=1:2:9
       for n=1:2:9
                  f=1/(n*m*sqrt(n^2+m^2))).*sin(m*pi*x).*sin(n*pi*y).*sin(t*sqrt(m^2+n^2));

       end
   end
z=(16/(pi^2))*f;

end