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Refactor mju_combineSparse to eliminate temporary buffers.

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Combine sparse vectors in-place by first counting total `nnz` and then working backwards from the end. This removes the need for temporary buffers in `mju_combineSparse` and its callers and speeds up the function by ~10%.

PiperOrigin-RevId: 902530210
Change-Id: I4f48c327103552ab968d3915399c6067367bec9f
This commit is contained in:
Yuval Tassa
2026-04-20 03:09:31 -07:00
committed by Copybara-Service
parent 3230cf99f9
commit e6d77650f7
8 changed files with 57 additions and 86 deletions
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src/engine/engine_solver.c
+5 -14
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@@ -829,8 +829,6 @@ typedef struct {
int* L_rowadr; // Hessian factor row addresses (nv x 1)
int* LT_rownnz; // Hessian factor transpose row nonzeros (nv x 1)
int* LT_rowadr; // Hessian factor transpose row addresses (nv x 1)
int* buf_ind; // index buffer for sparse addition (nv x 1)
mjtNum* buf_val; // value buffer for sparse addition (nv x 1)
// Newton arrays, computed-size (MakeHessian)
int nH; // number of nonzeros in Hessian H
@@ -979,9 +977,7 @@ static void PrimalAllocate(mjData* d, mjPrimalContext* ctx, int flg_Newton) {
if (flg_Newton) {
nNum += nefc + nv; // D, cholupd
if (is_elliptic) nNum += 6*nv; // LTJ
if (is_sparse) {
nNum += nv; // buf_val
} else {
if (!is_sparse) {
nNum += nv*nv; // L (dense)
if (is_elliptic) nNum += nv*nv; // Lcone (dense)
}
@@ -993,7 +989,7 @@ static void PrimalAllocate(mjData* d, mjPrimalContext* ctx, int flg_Newton) {
size_t nInt = nefc; // oldstate
if (is_sparse) {
nInt += 3*nv + nJ; // JT sparse
if (flg_Newton) nInt += 9*nv; // Newton sparse
if (flg_Newton) nInt += 8*nv; // Newton sparse
}
// allocate mjtNum and int blocks
@@ -1018,9 +1014,7 @@ static void PrimalAllocate(mjData* d, mjPrimalContext* ctx, int flg_Newton) {
if (is_elliptic) {
ctx->LTJ = numblock; numblock += 6*nv;
}
if (is_sparse) {
ctx->buf_val = numblock; numblock += nv;
} else {
if (!is_sparse) {
ctx->nL = nv*nv;
ctx->L = numblock; numblock += ctx->nL;
ctx->Lcone = is_elliptic ? numblock : NULL;
@@ -1049,7 +1043,6 @@ static void PrimalAllocate(mjData* d, mjPrimalContext* ctx, int flg_Newton) {
ctx->L_rowadr = intblock; intblock += nv;
ctx->LT_rownnz = intblock; intblock += nv;
ctx->LT_rowadr = intblock; intblock += nv;
ctx->buf_ind = intblock; intblock += nv;
}
// sparse: compute Jacobian transpose
@@ -1616,8 +1609,7 @@ static void MakeHessian(mjData* d, mjPrimalContext* ctx) {
// add mass matrix: H = J'*D*J + M
mju_addToMatSparse(ctx->H, ctx->H_rownnz, ctx->H_rowadr, ctx->H_colind, nv,
ctx->M, ctx->M_rownnz, ctx->M_rowadr, ctx->M_colind,
ctx->buf_val, ctx->buf_ind);
ctx->M, ctx->M_rownnz, ctx->M_rowadr, ctx->M_colind);
// compute H' sparse structure (upper triangle, required for symbolic Cholesky)
mju_transposeSparse(NULL, NULL, nv, nv, ctx->HT_rownnz, ctx->HT_rowadr, ctx->HT_colind, NULL,
@@ -1691,8 +1683,7 @@ static void FactorizeHessian(mjData* d, mjPrimalContext* ctx, int flg_recompute)
// add mass matrix: H = J'*D*J + C
mju_addToMatSparse(ctx->H, ctx->H_rownnz, ctx->H_rowadr, ctx->H_colind, nv,
ctx->M, ctx->M_rownnz, ctx->M_rowadr, ctx->M_colind,
ctx->buf_val, ctx->buf_ind);
ctx->M, ctx->M_rownnz, ctx->M_rowadr, ctx->M_colind);
}
// numeric sparse factorization: L = chol(H) using pre-computed sparsity pattern