Run the following program with the command（C:\Users\weiqi>FreeFem++ square.edp or C:\Users\weiqi>FreeFem+±mpi square.edp -wg), but the picture is white and has nothing.
mesh Th=square(20,20);
plot(Th);
load “metis”
//load “scotch”
//load “parmetis”
fespace Ph(Th,P0);
Ph color;
metisdual(color[],Th,4);
plot(color);
