mfem/linalg/blockvector.hpp

// Copyright (c) 2010-2025, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details.

#ifndef MFEM_BLOCKVECTOR
#define MFEM_BLOCKVECTOR

#include "../config/config.hpp"
#include "../general/array.hpp"
#include "vector.hpp"

namespace mfem
{

//! @class BlockVector
/**
 * \brief A class to handle Vectors in a block fashion
 *
 * All data is contained in Vector::data, while blockVector is just a viewer for
 * this data.
 *
 */
class BlockVector: public Vector
{
protected:

   //! Number of blocks in the blockVector
   int numBlocks;
   //! Offset for each block start. (length numBlocks+1)
   /**
    * blockOffsets[i+1] - blockOffsets[i] is the size of block i.
    *
    * This array is not owned.
    */
   const int *blockOffsets;
   //! array of Vector objects used to extract blocks without allocating memory.
   /** This array is owned. */
   Vector *blocks;

   void SetBlocks();

public:
   //! empty constructor
   BlockVector();

   //! Constructor
   /**
    * bOffsets is an array of integers (length nBlocks+1) that tells the offsets
    * of each block start.
    */
   BlockVector(const Array<int> & bOffsets);

   /// Construct a BlockVector with the given MemoryType @a mt.
   BlockVector(const Array<int> & bOffsets, MemoryType mt);

   //! Copy constructor
   BlockVector(const BlockVector & block);

   //! View constructor
   /**
    * data is an array of double of length at least blockOffsets[numBlocks] that
    * contain all the values of the monolithic vector.  bOffsets is an array of
    * integers (length nBlocks+1) that tells the offsets of each block start.
    * nBlocks is the number of blocks.
    */
   BlockVector(real_t *data, const Array<int> & bOffsets);

   /// Wrap a Vector as a BlockVector
   BlockVector(Vector &v, const Array<int> &bOffsets);

   /// Wrap a Vector as a BlockVector with offset
   BlockVector(Vector &v, int offset,  const Array<int> &bOffsets);

   //! Return the number of blocks
   int NumBlocks() const { return numBlocks; }

   //! Assignment operator. this and original must have the same block structure.
   BlockVector & operator=(const BlockVector & original);
   //! Set each entry of this equal to val
   BlockVector & operator=(real_t val);

   //! Destructor
   ~BlockVector();

   //! Get the i-th vector in the block.
   Vector & GetBlock(int i) { return blocks[i]; }
   //! Get the i-th vector in the block (const version).
   const Vector & GetBlock(int i) const { return blocks[i]; }

   //! Get the i-th vector in the block
   void GetBlockView(int i, Vector & blockView);

   int BlockSize(int i) { return blockOffsets[i+1] - blockOffsets[i]; }

   //! Update method
   /**
    * data is an array of double of length at least blockOffsets[numBlocks] that
    * contain all the values of the monolithic vector.  bOffsets is an array of
    * integers (length nBlocks+1) that tells the offsets of each block start.
    * nBlocks is the number of blocks.
    */
   void Update(real_t *data, const Array<int> & bOffsets);

   void Update(Vector & data, const Array<int> & bOffsets);

   /// Update a BlockVector with new @a bOffsets and make sure it owns its data.
   /** The block-vector will be re-allocated if either:
       - the offsets @a bOffsets are different from the current offsets, or
       - currently, the block-vector does not own its data. */
   void Update(const Array<int> &bOffsets);

   /** @brief Update a BlockVector with new @a bOffsets and make sure it owns
       its data and uses the MemoryType @a mt. */
   /** The block-vector will be re-allocated if either:
       - the offsets @a bOffsets are different from the current offsets, or
       - currently, the block-vector does not own its data, or
       - currently, the block-vector does not use MemoryType @a mt. */
   void Update(const Array<int> &bOffsets, MemoryType mt);

   /** @brief Synchronize the memory location flags (i.e. the memory validity
       flags) of the big/monolithic block-vector with its sub-vector blocks. The
       big/monolithic vector has the correct memory location flags. */
   /** This method will copy the data validity flags from the big/monolithic
       block-vector to its sub-vector block. */
   void SyncToBlocks() const;

   /** @brief Synchronize the memory location flags (i.e. the memory validity
       flags) of the big/monolithic block-vector with its sub-vector blocks. The
       sub-vector blocks have the correct memory location flags. */
   /** This method will copy/move the data of the sub-vector blocks (if
       necessary) so that each block matches the memory location flags of the
       big/monolithic block-vector. */
   void SyncFromBlocks() const;
};

}

#endif /* MFEM_BLOCKVECTOR */