Add CSR implementation of mj_factorI

PiperOrigin-RevId: 712498431
Change-Id: I13b52e53482ed97da8788875d4d95e2beb5ca7c1

src/engine/engine_core_smooth.h

@@ -51,6 +51,11 @@ MJAPI void mj_crb(const mjModel* m, mjData* d);
 // sparse L'*D*L factorizaton of inertia-like matrix M, assumed spd
 MJAPI void mj_factorI(const mjModel* m, mjData* d, const mjtNum* M, mjtNum* qLD, mjtNum* qLDiagInv);
 
+// sparse L'*D*L factorizaton of inertia-like matrix
+//  like mj_factorI, but using CSR representation
+MJAPI void mj_factorIs(mjtNum* mat, mjtNum* diaginv, int nv,
+                       const int* rownnz, const int* rowadr, const int* diagnum, const int* colind);
+
 // sparse L'*D*L factorizaton of the inertia matrix M, assumed spd
 MJAPI void mj_factorM(const mjModel* m, mjData* d);
 
@@ -61,8 +66,7 @@ MJAPI void mj_solveLD(const mjModel* m, mjtNum* x, int n,
 // in-place sparse backsubstitution:  x = inv(L'*D*L)*x
 //  like mj_solveLD, but using the CSR representation of L
 MJAPI void mj_solveLDs(mjtNum* x, const mjtNum* qLDs, const mjtNum* qLDiagInv, int nv,
-                       const int* rownnz, const int* rowadr, const int* diagind, const int* diagnum,
-                       const int* colind);
+                       const int* rownnz, const int* rowadr, const int* diagnum, const int* colind);
 
 // sparse backsubstitution:  x = inv(L'*D*L)*y, use factorization in d
 MJAPI void mj_solveM(const mjModel* m, mjData* d, mjtNum* x, const mjtNum* y, int n);