Relax a couple of assertions for empty matrices.

diff --git a/include/deal.II/lac/sparsity_pattern.h b/include/deal.II/lac/sparsity_pattern.h
index 2644d4597d67c639ac5ad2787cdbb56f982be210..ae5b6576ffe7d086d710a55367a409a7bd6444ce 100644 (file)
--- a/include/deal.II/lac/sparsity_pattern.h
+++ b/include/deal.II/lac/sparsity_pattern.h
@@ -1409,9 +1409,13 @@ inline
 std::size_t
 SparsityPattern::n_nonzero_elements () const
 {
-  Assert ((rowstart!=nullptr) && (colnums!=nullptr), ExcEmptyObject());
   Assert (compressed, ExcNotCompressed());
-  return rowstart[rows]-rowstart[0];
+
+  if ((rowstart!=nullptr) && (colnums!=nullptr))
+    return rowstart[rows]-rowstart[0];
+  else
+    // the object is empty or has zero size
+    return 0;
 }
 
 

diff --git a/source/lac/sparsity_pattern.cc b/source/lac/sparsity_pattern.cc
index 4051dffa4c4d87f5dd3e94d73d1a14637769edf0..c71504eee0059965fb51063199a60bbda2f9bfb7 100644 (file)
--- a/source/lac/sparsity_pattern.cc
+++ b/source/lac/sparsity_pattern.cc
@@ -356,7 +356,12 @@ SparsityPattern::reinit (const size_type m,
 void
 SparsityPattern::compress ()
 {
-  Assert ((rowstart!=nullptr) && (colnums!=nullptr), ExcEmptyObject());
+  // nothing to do if the object corresponds to an empty matrix
+  if ((rowstart==nullptr) && (colnums==nullptr))
+    {
+      compressed = true;
+      return;
+    }
 
   // do nothing if already compressed
   if (compressed)