Is there a direct way to calculate the number of boundary vertices? I know that for instance Th.nv gives the total number of vertices in the domain so I was wondering if there is a similar way to do it on boundary faces, if not how can I approach this problem?

Th.nbe gives you the total number of boundary elements from which you can get the vertex ID for each element. I need the total number of vertices which is basically the number of unique IDs.

For a simple closed curve boundary, you just call `Th.nbe`

as Julien suggested. And for those more complex cases, you can also use the following FreeFEM code and it’s fast

```
fespace Bh(Th, P1);
varf vGamma(u, v) = on(labels(Th), u=1);
real[int] gamma = vGamma(0, Bh, tgv=-1);
int nbv = gamma.sum;
```

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