From aadcd4d405224aad7be67c756eecb7d532cdb3ea Mon Sep 17 00:00:00 2001
From: Simon Sticko <simon.sticko@it.uu.se>
Date: Tue, 28 Mar 2017 10:45:45 +0200
Subject: [PATCH] Implement get_interpolation_matrix on FE_Nothing.

---
 include/deal.II/fe/fe_nothing.h | 10 ++++++++++
 source/fe/fe_nothing.cc         | 21 +++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/deal.II/fe/fe_nothing.h b/include/deal.II/fe/fe_nothing.h
index 34351ef5fe..8c98c12dc3 100644
--- a/include/deal.II/fe/fe_nothing.h
+++ b/include/deal.II/fe/fe_nothing.h
@@ -215,6 +215,16 @@ public:
   bool
   hp_constraints_are_implemented () const;
 
+  /**
+   * Return the matrix interpolating from the given finite element to the
+   * present one. Since the current finite element has no degrees of freedom, the
+   * interpolation matrix is necessarily empty.
+   */
+  virtual
+  void
+  get_interpolation_matrix (const FiniteElement<dim,spacedim> &source_fe,
+                            FullMatrix<double>       &interpolation_matrix) const;
+
   /**
    * Return the matrix interpolating from a face of of one element to the face
    * of the neighboring element. The size of the matrix is then
diff --git a/source/fe/fe_nothing.cc b/source/fe/fe_nothing.cc
index 3ed5782264..9a4fb88165 100644
--- a/source/fe/fe_nothing.cc
+++ b/source/fe/fe_nothing.cc
@@ -239,6 +239,27 @@ hp_constraints_are_implemented () const
 }
 
 
+
+template <int dim, int spacedim>
+void
+FE_Nothing<dim,spacedim>::
+get_interpolation_matrix (const FiniteElement<dim,spacedim> &/*source_fe*/,
+                          FullMatrix<double>       &interpolation_matrix) const
+{
+  // Since this element has no dofs,
+  // the interpolation matrix is necessarily empty.
+  (void)interpolation_matrix;
+
+  Assert (interpolation_matrix.m() == 0,
+          ExcDimensionMismatch (interpolation_matrix.m(),
+                                0));
+  Assert (interpolation_matrix.n() == 0,
+          ExcDimensionMismatch (interpolation_matrix.n(),
+                                0));
+}
+
+
+
 template <int dim, int spacedim>
 void
 FE_Nothing<dim,spacedim>::
-- 
2.39.5