From 908e7663d05c59ab254f4105c76c1392ce517430 Mon Sep 17 00:00:00 2001
From: Stefano Zampini <stefano.zampini@gmail.com>
Date: Tue, 24 Jan 2023 15:26:08 +0300
Subject: [PATCH] Convenience routine from IndexSet to PETSc IS

---
 include/deal.II/base/index_set.h |  9 +++++++++
 source/base/index_set.cc         | 22 ++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/deal.II/base/index_set.h b/include/deal.II/base/index_set.h
index e50f58439e..b17c18282c 100644
--- a/include/deal.II/base/index_set.h
+++ b/include/deal.II/base/index_set.h
@@ -37,6 +37,10 @@ DEAL_II_ENABLE_EXTRA_DIAGNOSTICS
 #  endif
 #endif
 
+#ifdef DEAL_II_WITH_PETSC
+#  include <petscis.h>
+#endif
+
 DEAL_II_NAMESPACE_OPEN
 
 /**
@@ -498,6 +502,11 @@ public:
 #  endif
 #endif
 
+#ifdef DEAL_II_WITH_PETSC
+  IS
+  make_petsc_is(const MPI_Comm &communicator = MPI_COMM_WORLD) const;
+#endif
+
 
   /**
    * Determine an estimate for the memory consumption (in bytes) of this
diff --git a/source/base/index_set.cc b/source/base/index_set.cc
index ef0a7c05e7..ecdad5d61f 100644
--- a/source/base/index_set.cc
+++ b/source/base/index_set.cc
@@ -17,6 +17,8 @@
 #include <deal.II/base/memory_consumption.h>
 #include <deal.II/base/mpi.h>
 
+#include <deal.II/lac/exceptions.h>
+
 #include <vector>
 
 #ifdef DEAL_II_WITH_TRILINOS
@@ -850,6 +852,26 @@ IndexSet::make_trilinos_map(const MPI_Comm &communicator,
 #endif
 
 
+#ifdef DEAL_II_WITH_PETSC
+IS
+IndexSet::make_petsc_is(const MPI_Comm &communicator) const
+{
+  std::vector<size_type> indices;
+  fill_index_vector(indices);
+
+  PetscInt              n = indices.size();
+  std::vector<PetscInt> pindices(indices.begin(), indices.end());
+
+  IS             is;
+  PetscErrorCode ierr =
+    ISCreateGeneral(communicator, n, pindices.data(), PETSC_COPY_VALUES, &is);
+  AssertThrow(ierr == 0, ExcPETScError(ierr));
+
+  return is;
+}
+#endif
+
+
 
 bool
 IndexSet::is_ascending_and_one_to_one(const MPI_Comm &communicator) const
-- 
2.39.5