// structured quadrilateral mesh
n = 4;
dx = 10.0/n;

Point(1) = {0, 0, 0, dx};
Point(2) = {10, 0, 0, dx};
Point(3) = {10, 10, 0, dx};
Point(4) = {0, 10, 0, dx};

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

Curve Loop(1) = {4, 1, 2, 3};
Plane Surface(1) = {1};

Periodic Curve{2} = {-4};
Periodic Curve{1} = {-3};

Recombine Surface {1};
Transfinite Surface {1};

Physical Surface(2) = {1};

Physical Curve (1) = {1};
Physical Curve (2) = {2};
Physical Curve (3) = {3};
Physical Curve (4) = {4};