MultiVector.h

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// ---------------------------------------------------------------------
//
// Copyright (c) 2017-2025  The Regents of the University of Michigan and DFT-FE
// authors.
//
// This file is part of the DFT-FE code.
//
// The DFT-FE code is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE at
// the top level of the DFT-FE distribution.
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//
 
 
/*
 * @author Sambit Das, Bikash Kanungo
 */
 
 
#ifndef dftfeMultiVector_h
#define dftfeMultiVector_h
 
#include <TypeConfig.h>
#include <MemoryStorage.h>
#include <MPIPatternP2P.h>
#include <MPICommunicatorP2P.h>
#include <memory>
#include <deal.II/lac/la_parallel_vector.h>
namespace dftfe
{
  namespace linearAlgebra
  {
    /**
     * @brief An class template to encapsulate a MultiVector.
     * A MultiVector is a collection of \f$N\f$ vectors belonging to the same
     * finite-dimensional vector space, where usual notion of vector size
     * denotes the dimension of the vector space. Note that this in the
     * mathematical sense and not in the sense of an multi-dimensional array.The
     * MultiVector is stored contiguously with the vector index being the
     * fastest index, or in other words a matrix of size \f$M \times N\f$ in row
     * major format with \f$M \f$ denoting the dimension of the vector space
     * (size of individual vector).
     *
     * This class handles both serial and distributed MultiVector
     * in a unfied way. There are different constructors provided for the
     * serial and distributed case.
     *
     * The serial MultiVector, as the name suggests, resides entirely in a
     * processor.
     *
     * The distributed MultiVector, on the other hand, is distributed across a
     * set of processors. The storage of each of the \f$N\f$ vectors in the
     * distributed MultiVector in a processor follows along similar lines to
     * a distributed Vector object and comprises of two parts:
     *   1. <b>locally owned part</b>: A part of the distribute MultiVector,
     * defined through a contiguous range of indices \f$[a,b)\f$ (\f$a\f$ is
     * included, but \f$b\f$ is not), for which the current processor is the
     * sole owner. The size of the locally owned part (i.e., \f$b-a\f$) is
     * termed as \e locallyOwnedSize. Note that the range of indices that
     * comprises the locally owned part (i.e., \f$[a,b)\f$) is same for all the
     * \f$N\f$ vectors in the MultiVector
     *   2. <b>ghost part</b>: Part of the MultiVector, defined
     *      through a set of ghost indices, that are owned by other processors.
     * The size of ghost indices for each vector is termed as \e ghostSize. Note
     * that the set of indices that define the ghost indices are same for all
     * the \f$N\f$ vectors in the MultiVector
     *
     * The global size of each vector in the distributed MultiVector
     * (i.e., the number of unique indices across all the processors) is simply
     * termed as \e size. Additionally, we define \e localSize = \e
     * locallyOwnedSize + \e ghostSize.
     *
     * We handle the serial MultiVector as a special case of the distributed
     * MultiVector, wherein \e size = \e locallyOwnedSize and \e ghostSize = 0.
     *
     * @note While typically one would link to an MPI library while compiling this class,
     * care is taken to seamlessly allow usage of this class even while not
     * linking to an MPI library. To do so, we have our own MPI wrappers that
     * redirect to the MPI library's function calls and definitions while
     * linking to an MPI library. While not linking to an MPI library, the MPI
     * wrappers provide equivalent functions and definitions that mimic the MPI
     * functions and definitions, albeit for a single processor. This allows the
     * user of this class to seamlessly switch between linking and de-linking to
     * an MPI library without any change in the code and with the expected
     * behavior.
     *
     * @note Note that the case of not linking to an MPI library and the case of
     * creating a serial mult-Vector are two independent things. One can still
     * create a serial MultiVector while linking to an MPI library and
     * running the code across multipe processors. That is, one can create a
     * serial MultiVector in one or more than one of the set of processors used
     * when running in parallel. Internally, we handle this by using
     * MPI_COMM_SELF as our MPI_Comm for the serial MultiVector (i.e., the
     * processor does self communication). However, while not linking to an MPI
     * library (which by definition means running on a single processor), there
     * is no notion of communication (neither with self nor with other
     * processors). In such case, both serial and distributed mult-Vector mean
     * the same thing and the MPI wrappers ensure the expected behavior (i.e.,
     * the behavior of a MultiVector while using just one processor)
     *
     * @tparam template parameter ValueType defines underlying datatype being stored
     *  in the MultiVector (i.e., dftfe::Int, double, complex<double>, etc.)
     * @tparam template parameter memorySpace defines the MemorySpace (i.e., HOST or
     * DEVICE) in which the MultiVector must reside.
     *
     * @note Broadly, there are two ways of constructing a distributed MultiVector.
     *  1. [<b>Prefered and efficient approach</b>] The first approach takes a
     *     pointer to an MPIPatternP2P as an input argument (along with other
     * arguments). The MPIPatternP2P, in turn, contains all the information
     *     regarding the locally owned and ghost part of the MultiVector as well
     * as the interaction map between processors. This is the most efficient way
     * of constructing a distributed MultiVector as it allows for reusing of an
     *     already constructed MPIPatternP2P.
     *  2. [<b> Expensive approach</b>] The second approach takes in the
     *     locally owned, ghost indices or the total number of indices
     *     across all the processors and internally creates an
     *     MPIPatternP2P object. Given that the creation of an MPIPatternP2P is
     *     expensive, this route of constructing a distributed MultiVector
     *     <b>should</b> be avoided.
     */
    template <typename ValueType, dftfe::utils::MemorySpace memorySpace>
    class MultiVector
    {
    public:
      //
      // typedefs
      //
      using Storage    = dftfe::utils::MemoryStorage<ValueType, memorySpace>;
      using value_type = typename Storage::value_type;
      using pointer    = typename Storage::pointer;
      using reference  = typename Storage::reference;
      using const_reference = typename Storage::const_reference;
      using iterator        = typename Storage::iterator;
      using const_iterator  = typename Storage::const_iterator;
 
    public:
      /**
       * @brief Default Constructor
       */
      MultiVector() = default;
 
      /**
       * @brief Default Destructor
       */
      ~MultiVector() = default;
 
      /**
       * @brief Constructor for \b serial MultiVector with vector size, number of vectors and initial value arguments
       * @param[in] size size of each vector in the MultiVector
       * @param[in] numVectors number of vectors in the MultiVector
       * @param[in] initVal initial value of elements of the MultiVector
       *
       */
      MultiVector(const dftfe::uInt size,
                  const dftfe::uInt numVectors,
                  const ValueType   initVal = 0);
 
      /**
       * @brief Constructor for a \serial MultiVector with a predefined
       * MultiVector::Storage (i.e., utils::MemoryStorage).
       * This constructor transfers the ownership of the input Storage to the
       * MultiVector. This is useful when one does not want to allocate new
       * memory and instead use memory allocated in the MultiVector::Storage
       * (i.e., utils::MemoryStorage).
       * The \e locallyOwnedSize, \e ghostSize, etc., are automatically set
       * using the size of the input Storage object.
       *
       * @param[in] storage unique_ptr to MultiVector::Storage whose ownership
       * is to be transfered to the MultiVector
       * @param[in] numVectors number of vectors in the MultiVector
       * @note This Constructor transfers the ownership from the input
       * unique_ptr \p storage to the internal data member of the MultiVector.
       * Thus, after the function call \p storage will point to NULL and any
       * access through \p storage will lead to <b>undefined behavior</b>.
       *
       */
      MultiVector(
        std::unique_ptr<typename MultiVector<ValueType, memorySpace>::Storage>
                    storage,
        dftfe::uInt numVectors);
 
      /**
       * @brief Constructor for a \b distributed MultiVector based on an input MPIPatternP2P.
       *
       * @param[in] mpiPatternP2P A shared_ptr to const MPIPatternP2P
       * based on which the distributed MultiVector will be created.
       * @param[in] numVectors number of vectors in the MultiVector
       * @param[in] initVal value with which the MultiVector shoud be
       * initialized
       */
      MultiVector(std::shared_ptr<const utils::mpi::MPIPatternP2P<memorySpace>>
                                    mpiPatternP2P,
                  const dftfe::uInt numVectors,
                  const ValueType   initVal = 0);
 
      /**
       * @brief Constructor for a \b distributed MultiVector with a predefined
       * MultiVector::Storage (i.e., utils::MemoryStorage) and MPIPatternP2P.
       * This constructor transfers the ownership of the input Storage to the
       * MultiVector. This is useful when one does not want to allocate new
       * memory and instead use memory allocated in the input
       * MultiVector::Storage (i.e., utils::MemoryStorage).
       *
       * @param[in] storage unique_ptr to MultiVector::Storage whose ownership
       * is to be transfered to the MultiVector
       * @param[in] mpiPatternP2P A shared_ptr to const MPIPatternP2P
       * based on which the distributed MultiVector will be created.
       * @param[in] numVectors number of vectors in the MultiVector
       *
       * @note This Constructor transfers the ownership from the input
       * unique_ptr \p storage to the internal data member of the MultiVector.
       * Thus, after the function call \p storage will point to NULL and any
       * access through \p storage will lead to <b>undefined behavior</b>.
       *
       */
      MultiVector(
        std::unique_ptr<typename MultiVector<ValueType, memorySpace>::Storage>
          &storage,
        std::shared_ptr<const utils::mpi::MPIPatternP2P<memorySpace>>
                          mpiPatternP2P,
        const dftfe::uInt numVectors);
 
      /**
       * @brief Constructor for a \distributed MultiVector based on locally
       * owned and ghost indices.
       * @note This way of construction is expensive. One should use the other
       * constructor based on an input MPIPatternP2P as far as possible.
       *
       * @param[in] locallyOwnedRange a pair \f$(a,b)\f$ which defines a range
       * of indices (continuous) that are owned by the current processor.
       * @param[in] ghostIndices vector containing an ordered set of ghost
       * indices (ordered in increasing order and non-repeating)
       * @param[in] mpiComm MPI_Comm object associated with the group
       * of processors across which the MultiVector is to be distributed
       * @param[in] numVectors number of vectors in the MultiVector
       * @param[in] initVal value with which the MultiVector shoud be
       * initialized
       *
       * @note The locallyOwnedRange should be an open interval where the start
       * index is included, but the end index is not included.
       */
      MultiVector(const std::pair<dftfe::uInt, dftfe::uInt> locallyOwnedRange,
                  const std::vector<dftfe::uInt>           &ghostIndices,
                  const MPI_Comm                           &mpiComm,
                  const dftfe::uInt                         numVectors,
                  ValueType                                 initVal = 0);
 
      /**
       * @brief Constructor for a special case of \b distributed MultiVector where none
       * none of the processors have any ghost indices.
       * @note This way of construction is expensive. One should use the other
       * constructor based on an input MPIPatternP2P as far as possible.
       *
       * @param[in] locallyOwnedRange a pair \f$(a,b)\f$ which defines a range
       * of indices (continuous) that are owned by the current processor.
       * @param[in] mpiComm MPI_Comm object associated with the group
       * of processors across which the MultiVector is to be distributed
       * @param[in] numVectors number of vectors in the MultiVector
       * @param[in] initVal value with which the MultiVector shoud be
       * initialized
       *
       * @note The locallyOwnedRange should be an open interval where the start index included,
       * but the end index is not included.
       */
      MultiVector(const std::pair<dftfe::uInt, dftfe::uInt> locallyOwnedRange,
                  const MPI_Comm                           &mpiComm,
                  const dftfe::uInt                         numVectors,
                  const ValueType                           initVal = 0);
 
 
      /**
       * @brief Constructor for a \b distributed MultiVector based on total number of global indices.
       * The resulting MultiVector will not contain any ghost indices on any of
       * the processors. Internally, the vector is divided to ensure as much
       * equitable distribution across all the processors much as possible.
       * @note This way of construction is expensive. One should use the other
       * constructor based on an input MPIPatternP2P as far as possible.
       * Further, the decomposition is not compatible with other ways of
       * distributed MultiVector construction.
       * @param[in] globalSize Total number of global indices that is
       * distributed over the processors.
       * @param[in] mpiComm MPI_Comm object associated with the group
       * of processors across which the MultiVector is to be distributed
       * @param[in] numVectors number of vectors in the MultiVector
       * @param[in] initVal value with which the MultiVector shoud be
       * initialized
       */
      MultiVector(const dftfe::uInt globalSize,
                  const MPI_Comm   &mpiComm,
                  const dftfe::uInt numVectors,
                  const ValueType   initVal = 0);
 
 
      /**
       * @brief Copy constructor
       * @param[in] u MultiVector object to copy from
       */
      MultiVector(const MultiVector &u);
 
      /**
       * @brief Copy constructor with reinitialisation
       * @param[in] u MultiVector object to copy from
       * @param[in] initVal Initial value of the MultiVector
       */
      MultiVector(const MultiVector &u, const ValueType initVal = 0);
 
      /**
       * @brief Move constructor
       * @param[in] u MultiVector object to move from
       */
      MultiVector(MultiVector &&u) noexcept;
 
      /**
       * @brief Copy assignment operator
       * @param[in] u const reference to MultiVector object to copy
       * from
       * @return reference to this object after copying data from u
       */
      MultiVector &
      operator=(const MultiVector &u);
 
      /**
       * @brief Move assignment operator
       * @param[in] u const reference to MultiVector object to move
       * from
       * @return reference to this object after moving data from u
       */
      MultiVector &
      operator=(MultiVector &&u);
 
      /**
       * @brief pointer swap
       *
       */
      void
      swap(MultiVector &u);
 
      /**
       * @brief reinit for a \b distributed MultiVector based on an input MPIPatternP2P.
       *
       * @param[in] mpiPatternP2P A shared_ptr to const MPIPatternP2P
       * based on which the distributed MultiVector will be reinitialized.
       * @param[in] numVectors number of vectors in the MultiVector
       * @param[in] initVal value with which the MultiVector shoud be
       * reinitialized
       */
      void
      reinit(std::shared_ptr<const utils::mpi::MPIPatternP2P<memorySpace>>
                               mpiPatternP2P,
             const dftfe::uInt numVectors,
             const ValueType   initVal = 0);
 
      /**
       * @brief reinit based on an input distributed MultiVector.
       *
       */
      void
      reinit(const MultiVector &u);
 
 
      /**
       * @brief Return iterator pointing to the beginning of MultiVector data.
       *
       * @returns Iterator pointing to the beginning of MultiVector.
       */
      iterator
      begin();
 
      /**
       * @brief Return iterator pointing to the beginning of MultiVector
       * data.
       *
       * @returns Constant iterator pointing to the beginning of
       * MultiVector.
       */
      const_iterator
      begin() const;
 
      /**
       * @brief Return iterator pointing to the end of MultiVector data.
       *
       * @returns Iterator pointing to the end of MultiVector.
       */
      iterator
      end();
 
      /**
       * @brief Return iterator pointing to the end of MultiVector data.
       *
       * @returns Constant iterator pointing to the end of
       * MultiVector.
       */
      const_iterator
      end() const;
 
      /**
       * @brief Return the raw pointer to the MultiVector data
       * @return pointer to data
       */
      ValueType *
      data();
 
      /**
       * @brief Return the constant raw pointer to the MultiVector data
       * @return pointer to const data
       */
      const ValueType *
      data() const;
 
 
      /**
       * @brief Set all entries of the MultiVector to a given value
       *
       * @param[in] val The value to which the entries are to be set
       */
      void
      setValue(const ValueType val);
 
      template <typename ValueBaseType>
      void
      scale(const ValueBaseType val);
 
      template <typename ValueBaseType>
      void
      add(const ValueBaseType *valVec, const MultiVector &u);
 
      template <typename ValueBaseType>
      void
      add(const ValueBaseType val, const MultiVector &u);
 
      template <typename ValueBaseType1, typename ValueBaseType2>
      void
      addAndScale(const ValueBaseType1 valScale,
                  const ValueBaseType2 valAdd,
                  const MultiVector   &u);
 
      template <typename ValueBaseType1, typename ValueBaseType2>
      void
      scaleAndAdd(const ValueBaseType1 valScale,
                  const ValueBaseType2 valAdd,
                  const MultiVector   &u);
 
      void
      dot(const MultiVector &u, ValueType *dotVec);
 
      void
      zeroOutGhosts();
 
      void
      updateGhostValues(const dftfe::uInt communicationChannel = 0);
 
      void
      accumulateAddLocallyOwned(const dftfe::uInt communicationChannel = 0);
 
      void
      updateGhostValuesBegin(const dftfe::uInt communicationChannel = 0);
 
      void
      updateGhostValuesEnd();
 
      void
      accumulateAddLocallyOwnedBegin(
        const dftfe::uInt communicationChannel = 0);
 
      void
      accumulateAddLocallyOwnedEnd();
 
      bool
      isCompatible(const MultiVector<ValueType, memorySpace> &rhs) const;
 
      std::shared_ptr<const utils::mpi::MPIPatternP2P<memorySpace>>
      getMPIPatternP2P() const;
 
      template <typename ValueBaseType>
      void
      l2Norm(ValueBaseType *normVec) const;
 
      void
      setCommunicationPrecision(
        utils::mpi::communicationPrecision commPrecision);
 
 
      dftfe::uInt
      globalSize() const;
      dftfe::uInt
      localSize() const;
      dftfe::uInt
      locallyOwnedSize() const;
      dftfe::uInt
      ghostSize() const;
      dftfe::uInt
      numVectors() const;
 
      const Storage &
      getData() const;
 
    private:
      std::unique_ptr<Storage> d_storage;
      dftfe::uInt              d_localSize;
      dftfe::uInt              d_globalSize;
      dftfe::uInt              d_locallyOwnedSize;
      dftfe::uInt              d_ghostSize;
      dftfe::uInt              d_numVectors;
      std::unique_ptr<utils::mpi::MPICommunicatorP2P<ValueType, memorySpace>>
        d_mpiCommunicatorP2P;
      std::shared_ptr<const utils::mpi::MPIPatternP2P<memorySpace>>
        d_mpiPatternP2P;
    };
 
    //
    // helper functions
    //
    template <typename ValueType, utils::MemorySpace memorySpace>
    void
    createMultiVectorFromDealiiPartitioner(
      const std::shared_ptr<const dealii::Utilities::MPI::Partitioner>
                                          &partitioner,
      const dftfe::uInt                    numVectors,
      MultiVector<ValueType, memorySpace> &multiVector);
 
  } // end of namespace linearAlgebra
} // end of namespace dftfe
#include "MultiVector.t.cc"
#endif // dftfeMultiVector_h