function f=greenf(x)
%Integrand for integrating Green's function over volume
global TAU N
g=x;
fac=x;
g=(2*sqrt(pi*TAU))^-N.*exp(-(x.^2)./(4*TAU));
switch N
case 1
   fac=2;
case 2
   fac=2*pi.*x;
case 3
   fac=4*pi.*x.^2;
end
f=g.*fac;

