Skip to content

[Type] Introduce function to compute the determinant of any square matrix #5877

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
fredroy merged 5 commits into from
Feb 9, 2026
Merged

[Type] Introduce function to compute the determinant of any square matrix #5877

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
2a4b912
[Type] Introduce function to compute the determinant of any square ma…
alxbilger Jan 21, 2026
f655f46
Make the funciton scalable and usable with sparse matrix (#9)
bakpaul Feb 5, 2026
5e64c27
[Type] Add unit test for determinant of 12x12 matrices
alxbilger Feb 5, 2026
c60201d
[Type] Refactor determinant computation with Gaussian elimination
alxbilger Feb 5, 2026
4f86c4b
Merge branch 'master' into generalizeddeterminant
fredroy Feb 9, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
21 changes: 21 additions & 0 deletions Sofa/framework/Type/src/sofa/type/Mat.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -914,6 +914,27 @@ class MatNoInit : public Mat<L,C,real>
}
};

template <sofa::Size N, typename real>
real determinant(const Mat<N, N, real>& mat)
{
real det = 0;
for (size_t p = 0; p < N; ++p)
{
Mat<N - 1, N - 1, real> submat;
for (size_t i = 1; i < N; ++i)
{
size_t colIndex = 0;
for (size_t j = 0; j < N; ++j)
{
if (j == p) continue;
submat(i - 1, colIndex++) = mat(i, j);
Copy link
Contributor

@bakpaul bakpaul Jan 21, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Wouldn't it be more efficient to only create a vector of col and row indices that is reduced of one element for each determinant development ? So in the end your 'submatrix' is like a view on the original matrix, instead of copying the same values multiple times ?

Copy link
Contributor Author

@alxbilger alxbilger Jan 21, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I did not try to reach high performances because I don't have the need. Currently, I use it only in init().

Copy link
Contributor

@hugtalbot hugtalbot Jan 23, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

would your changes be easily introduced @bakpaul ?
if yes, we can add it inside this PR
else, it could be done in a later one

Copy link
Contributor

@bakpaul bakpaul Jan 30, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yes I think so, I just need to take time to do it. Give me one week ?

Copy link
Contributor Author

@alxbilger alxbilger Feb 3, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Copy link
Contributor

@bakpaul bakpaul Feb 4, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

See alxbilger#9

}
}
det += ((p % 2 == 0) ? 1 : -1) * mat(0, p) * determinant(submat);
}
return det;
}

/// Determinant of a 3x3 matrix.
template<class real>
constexpr real determinant(const Mat<3,3,real>& m) noexcept
Expand Down
9 changes: 9 additions & 0 deletions Sofa/framework/Type/test/MatTypes_test.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -443,3 +443,12 @@ TEST(MatTypesTest, determinant3x3)
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<3,3,SReal>{{0, 1, 0}, {0, 0, 1}, {1, 0, 0}}), 1_sreal);
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<3,3,SReal>{{1, 1, 0}, {1, 0, 1}, {0, 1, 1}}), -2_sreal);
}

TEST(MatTypesTest, determinant4x4)
{
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<4,4,SReal>{{1,0,0,0}, {0,1,0,0}, {0,0,1,0}, {0,0,0,1}}), 1_sreal);
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<4,4,SReal>{{2,0,0,0}, {0,3,0,0}, {0,0,4,0}, {0,0,0,5}}), 120_sreal);
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<4,4,SReal>{{0,1,0,0}, {1,0,0,0}, {0,0,1,0}, {0,0,0,1}}), -1_sreal);
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<4,4,SReal>{{1,0,0,0}, {0,2,0,0}, {0,0,3,0}, {0,0,0,4}}), 24_sreal);
EXPECT_DOUBLE_EQ(sofa::type::determinant(sofa::type::Mat<4,4,SReal>{{1,3,5,9}, {1,3,1,7}, {4,3,9,7}, {5,2,0,9}}), -376_sreal);
}
Loading