add the possibility to solve for sparse rhs with Cholmod

Eigen/src/Sparse/SparseMatrix.h

@@ -78,6 +78,9 @@ class SparseMatrix
     typedef MappedSparseMatrix<Scalar,Flags> Map;
     using Base::IsRowMajor;
     typedef CompressedStorage<Scalar,Index> Storage;
+    enum {
+      Options = _Options
+    };
 
   protected:
 
@@ -436,6 +439,12 @@ class SparseMatrix
     {
       return Base::operator=(product);
     }
+    
+    template<typename OtherDerived>
+    EIGEN_STRONG_INLINE SparseMatrix& operator=(const ReturnByValue<OtherDerived>& func)
+    {
+      return Base::operator=(func);
+    }
     #endif
 
     template<typename OtherDerived>