Re: [petsc-users] Question about MATMPIAIJ and column indexes ordering
Added clarification to the man pages in https://gitlab.com/petsc/petsc/-/merge_requests/7170 > On Jan 8, 2024, at 4:31 AM, Deuse, Mathieu via petsc-users > wrote: > > Hello, > > I have a piece of code which generates a matrix in CSR format, but the > without sorting the column indexes in increasing order within each row. This > seems not to be 100% compatible with the MATMPIAIJ format: the documentation > of MatCreateMPIAIJWithArrays indeed mentions 'row-major ordering'. > > For example, consider the 2x2 matrix (1 2; 3 4), which in my code could be > stored as i=[0, 2, 4], j=[1, 0, 0, 1], v=[2, 1, 3, 4]. I can generate the > matrix as follows (on 1 proc): MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, 2, > 2, 2, 2, i, j, v, ). This appears to work fine, and I can then use the > matrix in a KSP for example. However, if I try to update the entry values > (same order and values v=[2, 1, 3, 4]) with MatUpdateMPIAIJWithArray(matrix, > v), it seems that PETSc does not memorize the order of the column indexes and > the matrix that I get now is (2 1; 3 4). I get the same result with > MatUpdateMPIAIJWithArrays(matrix, 2, 2, 2, 2, i, j, v). On the other hand, if > the column indexes are sorted within each row (i=[0, 2, 4], j=[0, 1, 0, 1], > v=[1, 2, 3, 4]), then it works fine. I have attached a minimal working > example (C++). > > Can I safely rely on MatCreateMPIAIJWithArrays working fine with unsorted > column indexes as long as I do not use MatUpdateMPIAIJWithArray(s)? Or should > I do the sorting myself before calling MatCreateMPIAIJWithArrays? (or > alternatively use another matrix format). > > Thanks in advance for the help. > > Kind regards, > > Mathieu Deuse >
Re: [petsc-users] Question about MATMPIAIJ and column indexes ordering
> On Jan 8, 2024, at 4:31 AM, Deuse, Mathieu via petsc-users > wrote: > > Hello, > > I have a piece of code which generates a matrix in CSR format, but the > without sorting the column indexes in increasing order within each row. This > seems not to be 100% compatible with the MATMPIAIJ format: the documentation > of MatCreateMPIAIJWithArrays indeed mentions 'row-major ordering'. > > For example, consider the 2x2 matrix (1 2; 3 4), which in my code could be > stored as i=[0, 2, 4], j=[1, 0, 0, 1], v=[2, 1, 3, 4]. I can generate the > matrix as follows (on 1 proc): MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, 2, > 2, 2, 2, i, j, v, ). This appears to work fine, and I can then use the > matrix in a KSP for example. However, if I try to update the entry values > (same order and values v=[2, 1, 3, 4]) with MatUpdateMPIAIJWithArray(matrix, > v), it seems that PETSc does not memorize the order of the column indexes and > the matrix that I get now is (2 1; 3 4). I get the same result with > MatUpdateMPIAIJWithArrays(matrix, 2, 2, 2, 2, i, j, v). On the other hand, if > the column indexes are sorted within each row (i=[0, 2, 4], j=[0, 1, 0, 1], > v=[1, 2, 3, 4]), then it works fine. I have attached a minimal working > example (C++). > > Can I safely rely on MatCreateMPIAIJWithArrays working fine with unsorted > column indexes as long as I do not use MatUpdateMPIAIJWithArray(s)? Yes, this is correct. The column indices do not need to be sorted if you never call MatUpdateMPIAIJWithArray(). > Or should I do the sorting myself before calling MatCreateMPIAIJWithArrays? > (or alternatively use another matrix format). > > Thanks in advance for the help. > > Kind regards, > > Mathieu Deuse >
[petsc-users] Question about MATMPIAIJ and column indexes ordering
Hello,
I have a piece of code which generates a matrix in CSR format, but the without
sorting the column indexes in increasing order within each row. This seems not
to be 100% compatible with the MATMPIAIJ format: the documentation of
MatCreateMPIAIJWithArrays indeed mentions 'row-major ordering'.
For example, consider the 2x2 matrix (1 2; 3 4), which in my code could be
stored as i=[0, 2, 4], j=[1, 0, 0, 1], v=[2, 1, 3, 4]. I can generate the
matrix as follows (on 1 proc): MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, 2, 2,
2, 2, i, j, v, ). This appears to work fine, and I can then use the
matrix in a KSP for example. However, if I try to update the entry values (same
order and values v=[2, 1, 3, 4]) with MatUpdateMPIAIJWithArray(matrix, v), it
seems that PETSc does not memorize the order of the column indexes and the
matrix that I get now is (2 1; 3 4). I get the same result with
MatUpdateMPIAIJWithArrays(matrix, 2, 2, 2, 2, i, j, v). On the other hand, if
the column indexes are sorted within each row (i=[0, 2, 4], j=[0, 1, 0, 1],
v=[1, 2, 3, 4]), then it works fine. I have attached a minimal working example
(C++).
Can I safely rely on MatCreateMPIAIJWithArrays working fine with unsorted
column indexes as long as I do not use MatUpdateMPIAIJWithArray(s)? Or should I
do the sorting myself before calling MatCreateMPIAIJWithArrays? (or
alternatively use another matrix format).
Thanks in advance for the help.
Kind regards,
Mathieu Deuse
#include
#include "petsc.h"
int main(int argc, char** argv)
{
PetscCall(PetscInitialize(, , nullptr, nullptr));
PetscIntm = 2;
PetscIntn = 2;
PetscInti[] = {0, 2, 4};
PetscIntj[] = {1, 0, 0, 1};
PetscScalar v[] = {2, 1, 3, 4};
Mat mat;
PetscCall(MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, m, n, m, n, i, j, v,
));
std::cout << "=== Before update ===" << std::endl;
for (PetscInt row = 0; row < m; ++row)
{
for (PetscInt col = 0; col < n; ++col)
{
PetscScalar x;
PetscCall(MatGetValue(mat, row, col, ));
std::cout << ' ' << x;
}
std::cout << std::endl;
}
PetscCall(MatUpdateMPIAIJWithArray(mat, v));
std::cout << "=== After update ===" << std::endl;
for (PetscInt row = 0; row < m; ++row)
{
for (PetscInt col = 0; col < n; ++col)
{
PetscScalar x;
PetscCall(MatGetValue(mat, row, col, ));
std::cout << ' ' << x;
}
std::cout << std::endl;
}
PetscCall(MatDestroy());
PetscCall(PetscFinalize());
}
