From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Wed, 21 Mar 2018 20:08:55 +0000 (-0600)
Subject: Relax a couple of assertions for empty matrices.
X-Git-Tag: v9.0.0-rc1~287^2~2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=85370f88cb052a336fb9ee8ec540f467eb113eab;p=dealii.git

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 2644d4597d..ae5b6576ff 100644
--- 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 4051dffa4c..c71504eee0 100644
--- 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)