vector n = (15,15,15);
vector a = (0,0,0);
vector b = (1,1,1);
mesh M = structured(n,a,b);

scene S = pov("void.pov");
domain Omega = domain(S);

function uexact=x*y*z;
function mu = 1;
function g = uexact-y*z;

solve(u) in Omega by M
{
  test(w)
  int(mu*grad(u)*grad(w)) + int(M xmin)(mu*u*w) = int(M xmin)(mu*g*w);
  u=uexact on M xmax;
  u=uexact on M ymin;
  u=uexact on M ymax;
  u=uexact on M zmin;
  u=uexact on M zmax;
}

double I = int(M)((u-uexact)^2);

cout << "error: " << sqrt(I) << "\n";
