message: Sort indices using an unstable sort in SMMP
  This is faster, non-allocating. And we're sorting a set so we really do
  not care for a stable sort.
diff: @@ -115,7 +115,7 @@ pub fn symbolic<Iptr: SpIndex, I: SpIndex>(
  }
  let c_start = c_indptr[a_row].index();
  let c_end = c_indptr[a_row + 1].index();
  - c_indices[c_start..c_end].sort();
  + c_indices[c_start..c_end].sort_unstable();
  }
  index[a_row] = sentinel0;
  }
  