a=2*pi;
s=2*pi/60;
[x,y,z]=meshgrid(-a:s:a,-a:s:a,-a:s:a);
cx = cos(2*x);
cy = cos(2*y);
cz = cos(2*z);
u = 10.0*(cos(x).*sin(y) + cos(y).*sin(z) + cos(z).*sin(x))- 0.5*(cx.*cy + cy.*cz + cz.*cx) - 14.0;
[f,v]=isosurface(u,0);
vertface2obj(v,f,'gyroid.obj')
