I'm a bit confused then. The following tests three get_view() with
IndexSets : your example (slightly modified), the example from the doc
of get_view(), and then a slight modification of it. Your example
returns 0-based indices, but the one from the doc returns 11 as first
index, which is 1-based. The last example throws an error. Is it just a
bug or am I missing something obvious?
Thanks,
Arthur
{
IndexSet A(10);
A.add_index(1);
A.add_index(2);
A.add_index(5);
std::cout << "A :";
A.print(std::cout);
IndexSet B(10);
B.add_index(0);
B.add_index(1);
B.add_index(4);
B.add_index(5);
B.add_index(6);
B.add_index(7);
B.add_index(8);
B.add_index(9);
std::cout << "B :";
B.print(std::cout);
IndexSet view = A.get_view(B);
std::cout << "View :";
view.print(std::cout);
}
{
const unsigned int N = 100;
IndexSet A(N);
A.add_range(20, 40);
std::cout << "A :";
A.print(std::cout);
// Odd numbers in [0,N)
IndexSet B(N);
for (unsigned int i = 1; i < N; i += 2)
B.add_index(i);
std::cout << "B :";
B.print(std::cout);
{
IndexSet view = A.get_view(B);
std::cout << "View B:";
view.print(std::cout);
}
IndexSet C(N);
C.add_index(22);
C.add_index(26);
std::cout << "C :";
C.print(std::cout);
{
IndexSet view = A.get_view(C);
std::cout << "View C :";
view.print(std::cout);
}
}
On 11/19/25 17:06, 'Wolfgang Bangerth' via deal.II User Group wrote:
On 11/19/25 14:05, Arthur Bawin wrote:
Then I try to re-create the constraints using get_view() and merge()
as indicated in affine_constraints.h :
You don't show the whole code, so it's difficult to say. But
get_view() doesn't just remove constraints outside the "viewed"
subset, but it re-enumerates. For example, if you have 10 DoFs and
your AffineConstraint stores constraints for indices 1, 2, 5. Then
let's say you call get_view() with an index (sub)set 4...8 inclusive,
then the result is not an AffineConstraint of size 10 that stores a
constraint for index 5. Rather, it is an AffineConstraint of size 5
that stores a constraint for index 1 (the second index within the
range 4...8).
Does that make sense as perhaps the cause for your issue?
Best
W.
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