Have sparse LU return permutation matrices rather than sparse matrices. This could well impact user code. It'd be interesting to see if there is any actual fall-out... Quite often, the permutation matrices are applied to *dense* vectors. Returning permutation matrices rather than sparse matrices is a slight performance enhancement, but likely lost in the noise.

--- a/liboctave/sparse-base-lu.h
+++ b/liboctave/sparse-base-lu.h
@@ -70,6 +70,10 @@
 
   ColumnVector Pr_vec (void) const;
 
+  PermMatrix Pc_mat (void) const;
+
+  PermMatrix Pr_mat (void) const;
+
   const octave_idx_type * row_perm (void) const { return P.fortran_vec (); }
 
   const octave_idx_type * col_perm (void) const { return Q.fortran_vec (); }