[Gmsh] Atypical, newbie question

Julius Bier Kirkegaard juliusbierk at gmail.com
Thu Mar 31 17:54:40 CEST 2016

```Dear all,

I have (I think) a fairly simple question, but it's also quite atypical, so
I have had no luck Googling. I hope that you one of you might have time to
point me in the right direction...

I have a box:

box_size = 50;
lb = 10.;
Point(1) = {-box_size/2, -box_size/2, -box_size/2, lb};
Point(2) = {box_size/2, -box_size/2, -box_size/2, lb};
Point(3) = {box_size/2, box_size/2, -box_size/2, lb};
Point(4) = {-box_size/2, box_size/2, -box_size/2, lb};
Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 4};
Line(4) = {4, 1};
Line Loop(5) = {1, 2, 3, 4};
Plane Surface(6) = {5};
Extrude {0, 0, box_size} {
Surface{6};
}

This works quite well and gmsh is happy to (3D) mesh it.

The problem is that I would to ensure that certain points inside the box
are node points. So my question is, how do I ensure that points, like these

lc = 10;
Point(5) = {7.150548, 1.000000,  -6.990684, lc};
Point(6) = {-4.438894, 1.000000,  -8.960816, lc};
Point(7) = {-9.893936, 1.000000,  1.452595, lc};
Point(8) = {-1.675894, 1.000000,  9.858569, lc};
Point(9) = {8.858176, 1.000000,  4.640336, lc};
Point(10) = {1.675894, 4.750000,  -9.858569, lc};
Point(11) = {-8.858176, 4.750000,  -4.640336, lc};
Point(12) = {-7.150548, 4.750000,  6.990684, lc};
Point(13) = {4.438894, 4.750000,  8.960816, lc};
Point(14) = {9.893936, 4.750000,  -1.452595, lc};
Point(15) = {7.150548, 8.500000,  -6.990684, lc};

are part of the mesh nodes?

The reason I need this is that I need to impose boundary conditions at
these specific points.