From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Wed, 27 Sep 2023 15:50:51 +0000 (-0600)
Subject: Add an assertion.
X-Git-Tag: relicensing~463^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4d1ba2ec65b933582604e71749921bc00de3e486;p=dealii.git

Add an assertion.
---

diff --git a/source/base/index_set.cc b/source/base/index_set.cc
index 168e1ecaa0..d9174be6b9 100644
--- a/source/base/index_set.cc
+++ b/source/base/index_set.cc
@@ -520,6 +520,13 @@ IndexSet::add_indices(const IndexSet &other, const size_type offset)
 bool
 IndexSet::is_subset_of(const IndexSet &other) const
 {
+  Assert(size() == other.size(),
+         ExcMessage("One index set can only be a subset of another if they "
+                    "describe index spaces of the same size. The ones in "
+                    "question here have sizes " +
+                    std::to_string(size()) + " and " +
+                    std::to_string(other.size()) + "."));
+
   // See whether there are indices in the current set that are not in 'other'.
   // If so, then this is clearly not a subset of 'other'.
   IndexSet A_minus_B = *this;