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mju_compressSparse(): add option to compress away small elements.

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PiperOrigin-RevId: 726010576
Change-Id: Ib6458037a5cf9a9d82abb364b7dda7aab2f36807
This commit is contained in:
Yuval Tassa
2025-02-12 05:07:18 -08:00
committed by Copybara-Service
parent faed1a1137
commit e39a5df06a
4 changed files with 62 additions and 14 deletions
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src/engine/engine_util_sparse.c
+22 -10
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@@ -438,22 +438,34 @@ int mju_addChains(int* res, int n, int NV1, int NV2,
// compress layout of sparse matrix
void mju_compressSparse(mjtNum* mat, int nr, int nc, int* rownnz, int* rowadr, int* colind) {
rowadr[0] = 0;
int adr = rownnz[0];
for (int r=1; r < nr; r++) {
// compress sparse matrix, remove elements with abs(value) <= minval, return total non-zeros
int mju_compressSparse(mjtNum* mat, int nr, int nc, int* rownnz, int* rowadr, int* colind,
mjtNum minval) {
int remove_small = minval >= 0;
int adr = 0;
for (int r=0; r < nr; r++) {
// save old rowadr, record new
int rowadr1 = rowadr[r];
int rowadr_old = rowadr[r];
rowadr[r] = adr;
// shift mat and mat_colind
for (int adr1=rowadr1; adr1 < rowadr1+rownnz[r]; adr1++) {
mat[adr] = mat[adr1];
colind[adr] = colind[adr1];
// shift mat and colind
int nnz = 0;
int end = rowadr_old + rownnz[r];
for (int adr_old=rowadr_old; adr_old < end; adr_old++) {
if (remove_small && mju_abs(mat[adr_old]) <= minval) {
continue;
}
if (adr != adr_old) {
mat[adr] = mat[adr_old];
colind[adr] = colind[adr_old];
}
adr++;
if (remove_small) nnz++;
}
if (remove_small) rownnz[r] = nnz;
}
return rowadr[nr-1] + rownnz[nr-1];
}