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Add mju_mulSymVecSparse, private engine function

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Multiply sparse symmetric matrix (only lower triangle represented) by vector

PiperOrigin-RevId: 752926934
Change-Id: I5aaae1266256aa88aee8c25e242b7a7c51ea8dd7
This commit is contained in:
Yuval Tassa
2025-04-29 16:32:49 -07:00
committed by Copybara-Service
parent 1766a388cc
commit 7742f62803
3 changed files with 80 additions and 0 deletions
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test/engine/engine_util_sparse_test.cc
+36
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@@ -1034,6 +1034,42 @@ TEST_F(EngineUtilSparseTest, MjuMulMatTVec) {
EXPECT_THAT(AsVector(res, 3), ElementsAre(5, 28, 24));
}
TEST_F(EngineUtilSparseTest, MjuMulSymVecSparse) {
constexpr int n = 4;
constexpr int nnz = 9;
mjtNum mat[n*n] = {1, 0, 0, 0,
-1, 2, 0, 0, // spurious (ignored) -1 at (1, 0)
3, 0, 4, 0,
5, 6, 7, 8};
// dense, full matrix
mjtNum sym[n*n] = {1, 0, 3, 5,
0, 2, 0, 6,
3, 0, 4, 7,
5, 6, 7, 8};
mjtNum mat_sparse[nnz];
int rownnz[n];
int rowadr[n];
int colind[nnz];
mju_dense2sparse(mat_sparse, mat, n, n, rownnz, rowadr, colind, nnz);
int diagnum[n] = {0, 1, 0, 0};
// multiply: res = (mat + strict_upper(mat')) * vec
mjtNum vec[n] = {4, 3, 2, 1};
mjtNum res[n];
mju_mulSymVecSparse(res, mat_sparse, vec, n, rownnz, rowadr, diagnum, colind);
// dense multiply
mjtNum res2[n];
mju_mulMatVec(res2, sym, vec, n, n);
for (int i=0; i < n; i++) {
EXPECT_EQ(res[i], res2[i]);
}
}
TEST_F(EngineUtilSparseTest, MjuDenseToSparse) {
int nr = 2;
int nc = 2;