From 7b902005de550cd52b3e6a423e7e62a79363acba Mon Sep 17 00:00:00 2001
From: Stefano Zampini <stefano.zampini@gmail.com>
Date: Tue, 17 Jan 2023 11:38:11 +0300
Subject: [PATCH] Remove usage of VecGetValues

It fails with the newest versions of PETSc if the vector is not assembled
---
 source/lac/petsc_vector_base.cc | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/source/lac/petsc_vector_base.cc b/source/lac/petsc_vector_base.cc
index 17c50e09b6..309fb0e361 100644
--- a/source/lac/petsc_vector_base.cc
+++ b/source/lac/petsc_vector_base.cc
@@ -108,9 +108,12 @@ namespace PETScWrappers
                     (index < static_cast<size_type>(end)),
                   ExcAccessToNonlocalElement(index, begin, end - 1));
 
-      PetscInt    idx = index;
-      PetscScalar value;
-      ierr = VecGetValues(vector.vector, 1, &idx, &value);
+      const PetscScalar *ptr;
+      PetscScalar        value;
+      ierr = VecGetArrayRead(vector.vector, &ptr);
+      AssertThrow(ierr == 0, ExcPETScError(ierr));
+      value = *(ptr + index - begin);
+      ierr  = VecRestoreArrayRead(vector.vector, &ptr);
       AssertThrow(ierr == 0, ExcPETScError(ierr));
 
       return value;
-- 
2.39.5