Move mju_cholFactorCount to engine_util_solve.

PiperOrigin-RevId: 746011856
Change-Id: If9812251420053644f4eca81adb5116d370ee524

src/engine/engine_util_sparse.c

@@ -795,55 +795,3 @@ void mju_sqrMatTDSparse(mjtNum* res, const mjtNum* mat, const mjtNum* matT,
 
   mj_freeStack(d);
 }
-
-// precount row non-zeros of reverse-Cholesky factor L, return total non-zeros
-//  based on ldl_symbolic from 'Algorithm 8xx: a concise sparse Cholesky factorization package'
-//  reads pattern from upper triangle
-int mju_cholFactorCount(int* L_rownnz, const int* rownnz, const int* rowadr, const int* colind,
-                        int n, mjData* d) {
-  mj_markStack(d);
-  int* parent = mjSTACKALLOC(d, n, int);
-  int* flag = mjSTACKALLOC(d, n, int);
-
-  // loop over rows in reverse order
-  for (int r = n - 1; r >= 0; r--) {
-    parent[r] = -1;
-    flag[r] = r;
-    L_rownnz[r] = 1;  // start with 1 for diagonal
-
-    // loop over non-zero columns of upper triangle
-    int start = rowadr[r];
-    int end = start + rownnz[r];
-    for (int c = start; c < end; c++) {
-      int i = colind[c];
-
-      // skip lower triangle
-      if (i <= r) {
-        continue;
-      }
-
-      // traverse from i to ancestor, stop when row is flagged
-      while (flag[i] != r) {
-        // if not yet set, set parent to current row
-        if (parent[i] == -1) {
-          parent[i] = r;
-        }
-
-        // increment non-zeros, flag row i, advance to parent
-        L_rownnz[i]++;
-        flag[i] = r;
-        i = parent[i];
-      }
-    }
-  }
-
-  mj_freeStack(d);
-
-  // sum up all row non-zeros
-  int nnz = 0;
-  for (int r = 0; r < n; r++) {
-    nnz += L_rownnz[r];
-  }
-
-  return nnz;
-}