Make DiagonalMatrix::restore_original_nonzero_pattern implementation consistent with doc

Author: lindsayad

include/numerics/diagonal_matrix.h

@@ -176,8 +176,7 @@ class DiagonalMatrix : public SparseMatrix<T>
 
   const NumericVector<T> & diagonal() const;
 
-  // Our nonzero pattern hasn't changed; it's always just the diagonal!
-  virtual void restore_original_nonzero_pattern() override {}
+  virtual void restore_original_nonzero_pattern() override;
 
 protected:
   /// Underlying diagonal matrix storage

src/numerics/diagonal_matrix.C

@@ -331,5 +331,12 @@ DiagonalMatrix<T>::diagonal() const
   return *_diagonal;
 }
 
+template <typename T>
+void
+DiagonalMatrix<T>::restore_original_nonzero_pattern()
+{
+  _diagonal->zero();
+}
+
 template class LIBMESH_EXPORT DiagonalMatrix<Number>;
 }