GMSH simple example physical groups

ex_groups_simple.geo

L = 1;
dx1 = 0.1*L;

Point(1) = {-0.5*L, -0.5*L, -0.5*L, dx1};
Point(2) = { 0.5*L, -0.5*L, -0.5*L, dx1};
Point(3) = { 0.5*L, -0.5*L,  0.5*L, dx1};
Point(4) = {-0.5*L, -0.5*L,  0.5*L, dx1};

Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 1};

ll = newl;
Line Loop(ll) = {1, 2, 3, 4};

sc = news;
Plane Surface(sc) = {ll};

ex = Extrude {0, 1*L, 0} { Surface{sc}; };

Printf("sc  %g", sc);       // base surface (front)
Printf("ex[0]  %g", ex[0]); // extruded surface (back)
Printf("ex[1]  %g", ex[1]); // volume
Printf("ex[2]  %g", ex[2]); // bottom
Printf("ex[3]  %g", ex[3]); // right
Printf("ex[4]  %g", ex[4]); // top
Printf("ex[5]  %g", ex[5]); // left

// number from 0 to N for FEniCS compatibility (?)
Physical Surface(0) = {sc};     // front
Physical Surface(1) = {ex[0]};  // back
Physical Surface(2) = {ex[2]};  // bottom
Physical Surface(3) = {ex[3]};  // right
Physical Surface(4) = {ex[4]};  // top
Physical Surface(5) = {ex[5]};  // left

Physical Volume(0) = {ex[1]};