reset_memory -> restore_original_nonzero_pattern

examples/miscellaneous/miscellaneous_ex17/miscellaneous_ex17.C

@@ -160,8 +160,8 @@ int main (int argc, char ** argv)
   // MatResetHash added in PETSc version 3.23
 #if !PETSC_VERSION_LESS_THAN(3, 23, 0)
   // reset the memory
-  // sys_matrix.reset_memory(); # See https://gitlab.com/petsc/petsc/-/merge_requests/8063
-  pre_matrix.reset_memory();
+  // sys_matrix.restore_original_nonzero_pattern(); # See https://gitlab.com/petsc/petsc/-/merge_requests/8063
+  pre_matrix.restore_original_nonzero_pattern();
   // zero
   sys_matrix.zero();
   pre_matrix.zero();

include/numerics/diagonal_matrix.h

@@ -176,6 +176,8 @@ class DiagonalMatrix : public SparseMatrix<T>
 
   const NumericVector<T> & diagonal() const;
 
+  virtual void restore_original_nonzero_pattern() override;
+
 protected:
   /// Underlying diagonal matrix storage
   std::unique_ptr<NumericVector<T>> _diagonal;

include/numerics/petsc_matrix.h

@@ -291,7 +291,7 @@ class PetscMatrix final : public PetscMatrixBase<T>
 
   virtual bool supports_hash_table() const override;
 
-  virtual void reset_memory() override;
+  virtual void restore_original_nonzero_pattern() override;
 
 protected:
   /**

include/numerics/sparse_matrix.h

@@ -606,9 +606,12 @@ class SparseMatrix : public ReferenceCountedObject<SparseMatrix<T>>,
   /**
    * Reset the memory storage of the matrix. Unlike \p clear(), this does not destroy the matrix but
    * rather will reset the matrix to use the original preallocation or when using hash table matrix
-   * assembly (see \p use_hash_table()) will reset (clear) the hash table used for assembly
+   * assembly (see \p use_hash_table()) will reset (clear) the hash table used for assembly. In the
+   * words of the \p MatResetPreallocation documentation in PETSc, 'current values in the matrix are
+   * lost in this call', so a user can expect to have back their original sparsity pattern in a
+   * zeroed state
    */
-  virtual void reset_memory() { libmesh_not_implemented(); }
+  virtual void restore_original_nonzero_pattern() { libmesh_not_implemented(); }
 
 protected:
   /**

src/numerics/diagonal_matrix.C

@@ -331,5 +331,12 @@ DiagonalMatrix<T>::diagonal() const
   return *_diagonal;
 }
 
+template <typename T>
+void
+DiagonalMatrix<T>::restore_original_nonzero_pattern()
+{
+  _diagonal->zero();
+}
+
 template class LIBMESH_EXPORT DiagonalMatrix<Number>;
 }

src/numerics/petsc_matrix.C

@@ -382,6 +382,8 @@ void PetscMatrix<T>::update_preallocation_and_zero ()
 template <typename T>
 void PetscMatrix<T>::reset_preallocation()
 {
+  semiparallel_only();
+
 #if !PETSC_VERSION_LESS_THAN(3,9,0)
   libmesh_assert (this->initialized());
 
@@ -1286,8 +1288,10 @@ PetscMatrix<T>::copy_from_hash ()
 
 template <typename T>
 void
-PetscMatrix<T>::reset_memory()
+PetscMatrix<T>::restore_original_nonzero_pattern()
 {
+  semiparallel_only();
+
   if (this->_use_hash_table)
 #if PETSC_RELEASE_GREATER_EQUALS(3, 23, 0)
     // This performs MatReset plus re-establishes the hash table