declare a ReverseInnerIterator in sparse CwiseBinaryOp. These ReverseInnerIterator should probably be removed anyway since we currently don't have real use cases for them. The only one in TriangularSolver could be advantageously replaced by a binary search.

Eigen/src/SparseCore/TriangularSolver.h

@@ -156,6 +156,7 @@ struct sparse_solve_triangular_selector<Lhs,Rhs,Mode,Upper,ColMajor>
         {
           if(!(Mode & UnitDiag))
           {
+            // TODO replace this by a binary search. make sure the binary search is safe for partially sorted elements
             typename Lhs::ReverseInnerIterator it(lhs, i);
             while(it && it.index()!=i)
               --it;