From: Marc Fehling <mafehling.git@gmail.com>
Date: Fri, 4 Mar 2022 05:30:28 +0000 (-0700)
Subject: Added `n_nonzero_elements` to PETSc `BlockSparseMatrix`.
X-Git-Tag: v9.4.0-rc1~406^2~2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7eb79d5f953d1bbb01884204b623efd349e1df5b;p=dealii.git

Added `n_nonzero_elements` to PETSc `BlockSparseMatrix`.
---

diff --git a/include/deal.II/lac/petsc_block_sparse_matrix.h b/include/deal.II/lac/petsc_block_sparse_matrix.h
index d7ebe0819c..60ac2c3e93 100644
--- a/include/deal.II/lac/petsc_block_sparse_matrix.h
+++ b/include/deal.II/lac/petsc_block_sparse_matrix.h
@@ -250,6 +250,14 @@ namespace PETScWrappers
       std::vector<IndexSet>
       locally_owned_range_indices() const;
 
+      /**
+       * Return the number of nonzero elements of this matrix. Actually, it
+       * returns the number of entries in the sparsity pattern; if any of the
+       * entries should happen to be zero, it is counted anyway.
+       */
+      size_type
+      n_nonzero_elements() const;
+
       /**
        * Return a reference to the MPI communicator object in use with this
        * matrix.
diff --git a/source/lac/petsc_parallel_block_sparse_matrix.cc b/source/lac/petsc_parallel_block_sparse_matrix.cc
index 598f3a57ff..0d0a553838 100644
--- a/source/lac/petsc_parallel_block_sparse_matrix.cc
+++ b/source/lac/petsc_parallel_block_sparse_matrix.cc
@@ -133,6 +133,17 @@ namespace PETScWrappers
       return index_sets;
     }
 
+    BlockSparseMatrix::size_type
+    BlockSparseMatrix::n_nonzero_elements() const
+    {
+      size_type n_nonzero = 0;
+      for (size_type rows = 0; rows < this->n_block_rows(); ++rows)
+        for (size_type cols = 0; cols < this->n_block_cols(); ++cols)
+          n_nonzero += this->block(rows, cols).n_nonzero_elements();
+
+      return n_nonzero;
+    }
+
     const MPI_Comm &
     BlockSparseMatrix::get_mpi_communicator() const
     {