Gmsh: what is the right syntax to iterate over a list of numbers with a For loop on the native language?

Question

I'm new to Gmsh and after browsing many sites I haven't found the answer for this silly error.

Using the native language of the software, I'm assigning a value to the Transfinite property of a bunch of lines (with no consecutive ID's) in my model, using this syntax:

value = 10;
For i In [81, 83, 85, 87, 72, 73, 75, 77, 79]
    Transfinite Curve{i} = value;
EndFor

When loading the file, in all the For loops on my script I get the same error message: "syntax error ([)". Documentation states the loop as:

For i In {1:3}
    x~{i} = i;
EndFor

followed by:

The brackets [] permit to extract one item from a list (parentheses can also be used instead of brackets).

It's still not really clear about my case, and the script seems to work but I prefer to be completely sure. Does anyone knows how to do in this case?

Thanks in advance.

Answer 1

It seems for-loops in gmsh are made for consecutive numbering only, so I would define an array to map from consecutive index numbers to arbitrary entity numbers.

lc = 1e-2;

Point(1) = {0 ,  0, 0, lc};
Point(2) = {.3,  0, 0, lc};
Point(3) = {.3, .1, 0, lc};
Point(4) = {0 , .1, 0, lc};

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

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

long_sides = {1, 3};   // this could be any numbers
long_side_divisions = 10; 
For i In {0:1}   // array indexing starts with zero
  Transfinite Curve(long_sides[i]) = long_side_divisions;
EndFor

short_sides = {2, 4}; 
short_side_divisions = 4; 
For i In {0:1} 
  Transfinite Curve(short_sides[i]) = short_side_divisions;
EndFor

Transfinite Surface{1}; 

Physical Curve(5) = {1, 2, 4}; 
Physical Surface("My surface") = {1};

Just for illustration, this example (save to mwe.geo and run gmsh -2 mwe.geo) creates a structured mesh on a rectangle with 3 elements along the short side and 9 along the long side. I hope this answers your question, because the syntax you looked up the documentation is about string generation (tilde becomes underscore).

P.S.: You do not need to count the items in the list manually, just use something like

number_of_short_sides = #short_sides[];
...
For i In {0:number_of_short_sides - 1}
...