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			/**
			* Copyright (©) 2016-2023 EPFL (Ecole Polytechnique Fédérale de Lausanne)
			* Laboratory (LSMS - Laboratoire de Simulation en Mécanique des Solides)
			*
			* This file is part of Akantu
			*
			* Akantu is free software: you can 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 3 of the License, or (at your option) any
			* later version.
			*
			* Akantu is distributed in the hope that it will be useful, but WITHOUT ANY
			* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
			* A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
			* details.
			*
			* You should have received a copy of the GNU Lesser General Public License
			* along with Akantu. If not, see <http://www.gnu.org/licenses/>.
			*/

			/* -------------------------------------------------------------------------- */
			#include "synchronizer_impl.hh"
			/* -------------------------------------------------------------------------- */

			namespace akantu {

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			SynchronizerImpl<Entity>::SynchronizerImpl(const Communicator & comm,
			const ID & id)

			: Synchronizer(comm, id), communications(comm) {}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			SynchronizerImpl<Entity>::SynchronizerImpl(const SynchronizerImpl & other,
			const ID & id)
			: Synchronizer(other), communications(other.communications) {
			this->id = id;
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::communicateOnce(
			const std::tuple<CommunicationSendRecv, CommunicationSendRecv> &
			send_recv_schemes,
			const Tag::CommTags & comm_tag, DataAccessor<Entity> & data_accessor,
			const SynchronizationTag & tag) const {
			// no need to synchronize
			if (this->nb_proc == 1) {
			return;
			}

			CommunicationSendRecv send_dir;
			CommunicationSendRecv recv_dir;
			std::tie(send_dir, recv_dir) = send_recv_schemes;

			using CommunicationRequests = std::vector<CommunicationRequest>;
			using CommunicationBuffers = std::map<Int, CommunicationBuffer>;

			CommunicationRequests send_requests;
			CommunicationRequests recv_requests;
			CommunicationBuffers send_buffers;
			CommunicationBuffers recv_buffers;

			auto postComm = [&](const auto & sr, auto & buffers,
			auto & requests) -> void {
			for (auto && pair : communications.iterateSchemes(sr)) {
			auto & proc = pair.first;
			const auto & scheme = pair.second;

			if (scheme.empty()) {
			continue;
			}

			auto & buffer = buffers[proc];

			auto buffer_size = data_accessor.getNbData(scheme, tag);
			if (buffer_size == 0) {
			continue;
			}

			#ifndef AKANTU_NDEBUG
			buffer_size += this->sanityCheckDataSize(scheme, tag, false);
			#endif

			buffer.resize(buffer_size);

			if (sr == recv_dir) {
			requests.push_back(communicator.asyncReceive(
			buffer, proc,
			Tag::genTag(this->rank, Int(tag), comm_tag, this->hash_id)));
			} else {
			#ifndef AKANTU_NDEBUG
			this->packSanityCheckData(buffer, scheme, tag);
			#endif
			data_accessor.packData(buffer, scheme, tag);

			AKANTU_DEBUG_ASSERT(
			buffer.getPackedSize() == buffer.size(),
			"The data accessor did not pack all the data it "
			"promised in communication with tag "
			<< tag << " (Promised: " << buffer.size()
			<< "bytes, packed: " << buffer.getPackedSize() << "bytes [avg: "
			<< Real(buffer.size() - buffer.getPackedSize()) / scheme.size()
			<< "bytes per entity missing])");

			send_requests.push_back(communicator.asyncSend(
			buffer, proc,
			Tag::genTag(proc, Int(tag), comm_tag, this->hash_id)));
			}
			}
			};

			// post the receive requests
			postComm(recv_dir, recv_buffers, recv_requests);

			// post the send data requests
			postComm(send_dir, send_buffers, send_requests);

			// treat the receive requests
			Idx request_ready{-1};
			while ((request_ready = Communicator::waitAny(recv_requests)) != -1) {
			auto & req = recv_requests[request_ready];
			auto proc = req.getSource();

			auto & buffer = recv_buffers[proc];
			const auto & scheme = this->communications.getScheme(proc, recv_dir);

			#ifndef AKANTU_NDEBUG
			this->unpackSanityCheckData(buffer, scheme, tag, proc, this->rank);
			#endif

			data_accessor.unpackData(buffer, scheme, tag);

			AKANTU_DEBUG_ASSERT(
			buffer.getLeftToUnpack() == 0,
			"The data accessor ignored some data in communication with tag "
			<< tag);

			req.free();
			recv_requests.erase(recv_requests.begin() + request_ready);
			}

			Communicator::waitAll(send_requests);
			Communicator::freeCommunicationRequest(send_requests);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::slaveReductionOnceImpl(
			DataAccessor<Entity> & data_accessor,
			const SynchronizationTag & tag) const {
			communicateOnce(std::make_tuple(_recv, _send), Tag::_reduce, data_accessor,
			tag);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::synchronizeOnceImpl(
			DataAccessor<Entity> & data_accessor,
			const SynchronizationTag & tag) const {
			communicateOnce(std::make_tuple(_send, _recv), Tag::_synchronize,
			data_accessor, tag);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::asynchronousSynchronizeImpl(
			const DataAccessor<Entity> & data_accessor,
			const SynchronizationTag & tag) {
			AKANTU_DEBUG_IN();

			if (not this->communications.hasCommunicationSize(tag)) {
			this->computeBufferSize(data_accessor, tag);
			}

			this->communications.incrementCounter(tag);

			// Posting the receive -------------------------------------------------------
			if (this->communications.hasPendingRecv(tag)) {
			AKANTU_CUSTOM_EXCEPTION_INFO(
			debug::CommunicationException(),
			"There must still be some pending receive communications."
			<< " Tag is " << tag << " Cannot start new ones");
			}

			for (auto && comm_desc : this->communications.iterateRecv(tag)) {
			comm_desc.postRecv(this->hash_id);
			}

			// Posting the sends -------------------------------------------------------
			if (communications.hasPendingSend(tag)) {
			AKANTU_CUSTOM_EXCEPTION_INFO(
			debug::CommunicationException(),
			"There must be some pending sending communications."
			<< " Tag is " << tag);
			}

			for (auto && comm_desc : this->communications.iterateSend(tag)) {
			comm_desc.resetBuffer();

			#ifndef AKANTU_NDEBUG
			this->packSanityCheckData(comm_desc);
			#endif

			comm_desc.packData(data_accessor);
			comm_desc.postSend(this->hash_id);
			}

			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::waitEndSynchronizeImpl(
			DataAccessor<Entity> & data_accessor, const SynchronizationTag & tag) {
			AKANTU_DEBUG_IN();

			#ifndef AKANTU_NDEBUG
			if (this->communications.begin(tag, _recv) !=
			this->communications.end(tag, _recv) &&
			!this->communications.hasPendingRecv(tag)) {
			AKANTU_CUSTOM_EXCEPTION_INFO(debug::CommunicationException(),
			"No pending communication with the tag \""
			<< tag);
			}
			#endif

			auto recv_end = this->communications.end(tag, _recv);
			decltype(recv_end) recv_it;

			while ((recv_it = this->communications.waitAnyRecv(tag)) != recv_end) {
			auto && comm_desc = *recv_it;
			#ifndef AKANTU_NDEBUG
			this->unpackSanityCheckData(comm_desc);
			#endif

			comm_desc.unpackData(data_accessor);
			comm_desc.resetBuffer();
			comm_desc.freeRequest();
			}

			this->communications.waitAllSend(tag);
			this->communications.freeSendRequests(tag);

			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::computeAllBufferSizes(
			const DataAccessor<Entity> & data_accessor) {
			for (auto && tag : this->communications.iterateTags()) {
			this->computeBufferSize(data_accessor, tag);
			}
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::computeBufferSizeImpl(
			const DataAccessor<Entity> & data_accessor,
			const SynchronizationTag & tag) {
			AKANTU_DEBUG_IN();

			if (not this->communications.hasCommunication(tag)) {
			this->communications.initializeCommunications(tag);
			AKANTU_DEBUG_ASSERT(communications.hasCommunication(tag) == true,
			"Communications where not properly initialized");
			}

			for (auto sr : iterate_send_recv) {
			for (auto && [proc, scheme] : this->communications.iterateSchemes(sr)) {
			Int size{0};
			#ifndef AKANTU_NDEBUG
			size += this->sanityCheckDataSize(scheme, tag);
			#endif
			size += data_accessor.getNbData(scheme, tag);
			AKANTU_DEBUG_INFO("I have "
			<< size << "(" << printMemorySize<char>(size) << " - "
			<< scheme.size() << " element(s)) data to "
			<< std::string(sr == _recv ? "receive from" : "send to")
			<< proc << " for tag " << tag);

			this->communications.setCommunicationSize(tag, proc, size, sr);
			}
			}
			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <typename Entity> void SynchronizerImpl<Entity>::reset() {
			AKANTU_DEBUG_IN();
			communications.resetSchemes();
			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <typename Entity>
			template <typename Pred>
			void SynchronizerImpl<Entity>::split(SynchronizerImpl<Entity> & in_synchronizer,
			Pred && pred) {
			AKANTU_DEBUG_IN();

			auto filter_list = [&](auto & list, auto & new_list) {
			auto copy = list;
			list.resize(0);
			new_list.resize(0);

			for (auto && entity : copy) {
			if (std::forward<Pred>(pred)(entity)) {
			new_list.push_back(entity);
			} else {
			list.push_back(entity);
			}
			}
			};

			for (auto sr : iterate_send_recv) {
			for (auto & scheme_pair :
			in_synchronizer.communications.iterateSchemes(sr)) {
			auto proc = scheme_pair.first;
			auto & scheme = scheme_pair.second;
			auto & new_scheme = communications.createScheme(proc, sr);
			filter_list(scheme, new_scheme);
			}
			}

			in_synchronizer.communications.invalidateSizes();
			communications.invalidateSizes();

			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <typename Entity>
			template <typename Updater>
			void SynchronizerImpl<Entity>::updateSchemes(Updater && scheme_updater) {
			for (auto sr : iterate_send_recv) {
			for (auto & scheme_pair : communications.iterateSchemes(sr)) {
			auto proc = scheme_pair.first;
			auto & scheme = scheme_pair.second;
			std::forward<Updater>(scheme_updater)(scheme, proc, sr);
			}
			}

			communications.invalidateSizes();
			}

			/* -------------------------------------------------------------------------- */
			template <typename Entity>
			template <typename Pred>
			void SynchronizerImpl<Entity>::filterScheme(Pred && pred) {
			std::vector<CommunicationRequest> requests;
			std::unordered_map<Idx, Array<Idx>> keep_entities;

			auto filter_list = [](const auto & keep, auto & list) {
			Array<Entity> new_list;
			for (const auto & keep_entity : keep) {
			const Entity & entity = list(keep_entity);
			new_list.push_back(entity);
			}
			list.copy(new_list);
			};

			// loop over send_schemes
			for (auto & scheme_pair : communications.iterateSchemes(_recv)) {
			auto proc = scheme_pair.first;
			auto & scheme = scheme_pair.second;

			auto & keep_entity = keep_entities[proc];
			for (auto && entity : enumerate(scheme)) {
			if (pred(std::get<1>(entity))) {
			keep_entity.push_back(std::get<0>(entity));
			}
			}

			auto tag = Tag::genTag(this->rank, 0, Tag::_modify_scheme);
			AKANTU_DEBUG_INFO("I have " << keep_entity.size()
			<< " elements to still receive from processor "
			<< proc << " (communication tag : " << tag
			<< ")");

			filter_list(keep_entity, scheme);
			requests.push_back(communicator.asyncSend(keep_entity, proc, tag));
			}

			// clean the receive scheme
			for (auto & scheme_pair : communications.iterateSchemes(_send)) {
			auto proc = scheme_pair.first;
			auto & scheme = scheme_pair.second;

			auto tag = Tag::genTag(proc, 0, Tag::_modify_scheme);
			AKANTU_DEBUG_INFO("Waiting list of elements to keep from processor "
			<< proc << " (communication tag : " << tag << ")");

			CommunicationStatus status;
			communicator.probe<Int>(proc, tag, status);

			Array<Int> keep_entity(status.size(), 1, "keep_element");
			AKANTU_DEBUG_INFO("I have "
			<< keep_entity.size()
			<< " elements to keep in my send list to processor "
			<< proc << " (communication tag : " << tag << ")");

			communicator.receive(keep_entity, proc, tag);

			filter_list(keep_entity, scheme);
			}

			Communicator::waitAll(requests);
			Communicator::freeCommunicationRequest(requests);
			communications.invalidateSizes();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity> void SynchronizerImpl<Entity>::swapSendRecv() {
			communications.swapSendRecv();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::copySchemes(const SynchronizerImpl & other) {
			reset();

			for (auto sr : iterate_send_recv) {
			for (auto & scheme_pair : other.communications.iterateSchemes(sr)) {
			auto proc = scheme_pair.first;
			auto & other_scheme = scheme_pair.second;
			auto & scheme = communications.createScheme(proc, sr);
			scheme.copy(other_scheme);
			}
			}
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			SynchronizerImpl<Entity> &
			SynchronizerImpl<Entity>::operator=(const SynchronizerImpl & other) {
			copySchemes(other);
			return *this;
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			Int SynchronizerImpl<Entity>::sanityCheckDataSize(
			const Array<Entity> & /unused/, const SynchronizationTag & /unused/,
			bool is_comm_desc) const {
			if (not is_comm_desc) {
			return 0;
			}

			Int size = 0;
			size += sizeof(SynchronizationTag); // tag
			size += sizeof(Int); // comm_desc.getNbData();
			size += sizeof(Int); // comm_desc.getProc();
			size += sizeof(this->rank); // mesh.getCommunicator().whoAmI();

			return size;
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::packSanityCheckData(
			CommunicationDescriptor<Entity> & comm_desc) const {
			auto & buffer = comm_desc.getBuffer();
			buffer << comm_desc.getTag();
			buffer << comm_desc.getNbData();
			buffer << comm_desc.getProc();
			buffer << this->rank;

			const auto & tag = comm_desc.getTag();
			const auto & send_element = comm_desc.getScheme();

			this->packSanityCheckData(buffer, send_element, tag);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::unpackSanityCheckData(
			CommunicationDescriptor<Entity> & comm_desc) const {
			auto & buffer = comm_desc.getBuffer();
			const auto & tag = comm_desc.getTag();

			auto nb_data = comm_desc.getNbData();
			auto proc = comm_desc.getProc();
			auto rank = this->rank;

			decltype(nb_data) recv_nb_data;
			decltype(proc) recv_proc;
			decltype(rank) recv_rank;

			SynchronizationTag t{0};
			buffer >> t;
			buffer >> recv_nb_data;
			buffer >> recv_proc;
			buffer >> recv_rank;

			AKANTU_DEBUG_ASSERT(
			t == tag, "The tag received does not correspond to the tag expected");

			AKANTU_DEBUG_ASSERT(
			nb_data == recv_nb_data,
			"The nb_data received does not correspond to the nb_data expected");

			AKANTU_DEBUG_ASSERT(recv_rank == proc,
			"The rank received does not correspond to the proc");

			AKANTU_DEBUG_ASSERT(recv_proc == rank,
			"The proc received does not correspond to the rank");

			auto & recv_element = comm_desc.getScheme();
			this->unpackSanityCheckData(buffer, recv_element, tag, proc, rank);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity> bool SynchronizerImpl<Entity>::hasChanged() {
			communicator.allReduce(entities_changed, SynchronizerOperation::_lor);
			return entities_changed;
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			void SynchronizerImpl<Entity>::initScatterGatherCommunicationScheme() {
			if (this->nb_proc == 1) {
			entities_changed = false;
			AKANTU_DEBUG_OUT();
			return;
			}

			AKANTU_TO_IMPLEMENT();
			}

			/* -------------------------------------------------------------------------- */
			template <>
			inline void SynchronizerImpl<Idx>::initScatterGatherCommunicationScheme() {
			if (this->nb_proc == 1) {
			entities_changed = false;
			return;
			}

			this->entities_from_root.clear();
			this->master_receive_entities.clear();

			Array<Idx> entities_to_send;
			fillEntityToSend(entities_to_send);

			std::vector<CommunicationRequest> requests;

			if (this->rank == Int(this->root)) {
			master_receive_entities[this->root].copy(entities_to_send);

			Array<Idx> nb_entities_per_proc(this->nb_proc);
			communicator.gather(entities_to_send.size(), nb_entities_per_proc);

			for (Int p = 0; p < nb_proc; ++p) {
			if (p == Int(this->root)) {
			continue;
			}

			auto & receive_per_proc = master_receive_entities[p];
			receive_per_proc.resize(nb_entities_per_proc(p));
			if (nb_entities_per_proc(p) == 0) {
			continue;
			}

			requests.push_back(communicator.asyncReceive(
			receive_per_proc, p,
			Tag::genTag(p, 0, Tag::_gather_initialization, this->hash_id)));
			}
			} else {
			communicator.gather(entities_to_send.size(), this->root);
			AKANTU_DEBUG(dblDebug, "I have " << entities_to_send.size()
			<< " entities to send to master proc");

			if (not entities_to_send.empty()) {
			requests.push_back(communicator.asyncSend(
			entities_to_send, this->root,
			Tag::genTag(this->rank, 0, Tag::_gather_initialization,
			this->hash_id)));
			}
			}

			entities_changed = false;
			Communicator::waitAll(requests);
			Communicator::freeCommunicationRequest(requests);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			template <typename T>
			void SynchronizerImpl<Entity>::gather(const Array<T> & to_gather,
			Array<T> & gathered) {
			if (this->hasChanged()) {
			initScatterGatherCommunicationScheme();
			}

			AKANTU_DEBUG_ASSERT(this->rank == this->root,
			"This function cannot be called on a slave processor");
			AKANTU_DEBUG_ASSERT(to_gather.size() == this->canScatterSize(),
			"The array to gather does not have the correct size");
			AKANTU_DEBUG_ASSERT(gathered.size() == this->gatheredSize(),
			"The gathered array does not have the correct size");

			if (this->nb_proc == 1) {
			gathered.copy(to_gather, true);

			AKANTU_DEBUG_OUT();
			return;
			}

			std::map<Int, CommunicationBuffer> buffers;
			std::vector<CommunicationRequest> requests;
			for (Int p = 0; p < this->nb_proc; ++p) {
			if (p == this->root) {
			continue;
			}

			auto receive_it = this->master_receive_entities.find(p);
			AKANTU_DEBUG_ASSERT(receive_it != this->master_receive_entities.end(),
			"Could not find the receive list for dofs of proc "
			<< p);
			const auto & receive_entities = receive_it->second;
			if (receive_entities.empty()) {
			continue;
			}

			auto & buffer = buffers[p];

			buffer.resize(receive_entities.size() * to_gather.getNbComponent() *
			sizeof(T));

			AKANTU_DEBUG_INFO(
			"Preparing to receive data for "
			<< receive_entities.size() << " entities from processor " << p << " "
			<< Tag::genTag(p, this->root, Tag::_gather, this->hash_id));

			requests.push_back(communicator.asyncReceive(
			buffer, p, Tag::genTag(p, this->root, Tag::_gather, this->hash_id)));
			}

			auto data_gathered_it = gathered.begin(to_gather.getNbComponent());

			{ // copy master data
			auto data_to_gather_it = to_gather.begin(to_gather.getNbComponent());
			for (auto local_entity : entities_from_root) {
			auto global_entity = localToGlobalEntity(local_entity);

			auto && entity_data_gathered = data_gathered_it[global_entity];
			auto && entity_data_to_gather = data_to_gather_it[local_entity];
			entity_data_gathered = entity_data_to_gather;
			}
			}

			auto rr = -1;
			while ((rr = Communicator::waitAny(requests)) != -1) {
			auto & request = requests[rr];
			auto sender = request.getSource();

			AKANTU_DEBUG_ASSERT(this->master_receive_entities.find(sender) !=
			this->master_receive_entities.end() &&
			buffers.find(sender) != buffers.end(),
			"Missing infos concerning proc " << sender);

			const auto & receive_entities =
			this->master_receive_entities.find(sender)->second;
			auto & buffer = buffers[sender];

			for (auto global_entity : receive_entities) {
			auto && entity_data = data_gathered_it[global_entity];
			buffer >> entity_data;
			}

			requests.erase(requests.begin() + rr);
			}
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			template <typename T>
			void SynchronizerImpl<Entity>::gather(const Array<T> & to_gather) {
			AKANTU_DEBUG_IN();

			if (this->hasChanged()) {
			initScatterGatherCommunicationScheme();
			}

			AKANTU_DEBUG_ASSERT(this->rank != this->root,
			"This function cannot be called on the root processor");
			AKANTU_DEBUG_ASSERT(to_gather.size() == this->canScatterSize(),
			"The array to gather does not have the correct size");

			if (this->entities_from_root.empty()) {
			AKANTU_DEBUG_OUT();
			return;
			}
			CommunicationBuffer buffer(this->entities_from_root.size() *
			to_gather.getNbComponent() * sizeof(T));

			auto data_it = to_gather.begin(to_gather.getNbComponent());
			for (auto entity : this->entities_from_root) {
			auto && data = data_it[entity];
			buffer << data;
			}

			AKANTU_DEBUG_INFO("Gathering data for "
			<< to_gather.size() << " dofs on processor " << this->root
			<< " "
			<< Tag::genTag(this->rank, 0, Tag::_gather, this->hash_id));

			communicator.send(buffer, this->root,
			Tag::genTag(this->rank, 0, Tag::_gather, this->hash_id));

			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			template <typename T>
			void SynchronizerImpl<Entity>::scatter(Array<T> & scattered,
			const Array<T> & to_scatter) {
			AKANTU_DEBUG_IN();

			if (this->hasChanged()) {
			initScatterGatherCommunicationScheme();
			}

			AKANTU_DEBUG_ASSERT(this->rank == this->root,
			"This function cannot be called on a slave processor");
			AKANTU_DEBUG_ASSERT(scattered.size() == this->canScatterSize(),
			"The scattered array does not have the correct size");
			AKANTU_DEBUG_ASSERT(to_scatter.size() == this->gatheredSize(),
			"The array to scatter does not have the correct size");

			if (this->nb_proc == 1) {
			scattered.copy(to_scatter, true);
			AKANTU_DEBUG_OUT();
			return;
			}

			std::map<Idx, CommunicationBuffer> buffers;
			std::vector<CommunicationRequest> requests;

			for (Int p = 0; p < nb_proc; ++p) {
			auto data_to_scatter_it = to_scatter.begin(to_scatter.getNbComponent());

			if (p == this->rank) {
			auto data_scattered_it = scattered.begin(to_scatter.getNbComponent());

			// copy the data for the local processor
			for (auto local_entity : entities_from_root) {
			auto global_entity = localToGlobalEntity(local_entity);
			data_scattered_it[local_entity] = data_to_scatter_it[global_entity];
			}

			continue;
			}

			const auto & receive_entities =
			this->master_receive_entities.find(p)->second;

			// prepare the send buffer
			auto & buffer = buffers[p];
			buffer.resize(receive_entities.size() * scattered.getNbComponent() *
			sizeof(T));

			// pack the data
			for (auto global_entity : receive_entities) {
			auto && entity_data_to_scatter = data_to_scatter_it[global_entity];
			buffer << entity_data_to_scatter;
			}

			// send the data
			requests.push_back(communicator.asyncSend(
			buffer, p, Tag::genTag(p, 0, Tag::_scatter, this->hash_id)));
			}

			// wait a clean communications
			Communicator::waitAll(requests);
			Communicator::freeCommunicationRequest(requests);

			// synchronize slave and ghost nodes
			synchronizeArray(scattered);

			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			template <typename T>
			void SynchronizerImpl<Entity>::scatter(Array<T> & scattered) {
			AKANTU_DEBUG_IN();

			if (this->hasChanged()) {
			this->initScatterGatherCommunicationScheme();
			}

			AKANTU_DEBUG_ASSERT(this->rank != this->root,
			"This function cannot be called on the root processor");
			AKANTU_DEBUG_ASSERT(scattered.size() == this->canScatterSize(),
			"The scattered array does not have the correct size");

			// prepare the data
			auto data_scattered_it = scattered.begin(scattered.getNbComponent());
			CommunicationBuffer buffer(this->entities_from_root.size() *
			scattered.getNbComponent() * sizeof(T));

			// receive the data
			communicator.receive(
			buffer, this->root,
			Tag::genTag(this->rank, 0, Tag::_scatter, this->hash_id));

			// unpack the data
			for (auto local_entity : entities_from_root) {
			auto && data_scattered = data_scattered_it[local_entity];
			buffer >> data_scattered;
			}

			// synchronize the ghosts
			synchronizeArray(scattered);

			AKANTU_DEBUG_OUT();
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			template <typename T>
			void SynchronizerImpl<Entity>::synchronizeArray(Array<T> & array) const {
			static_assert(std::is_same<Entity, Idx>::value,
			"Not implemented for other type than Idx");
			SimpleIdxDataAccessor<T> data_accessor(array, SynchronizationTag::_whatever);
			this->synchronizeOnce(data_accessor, SynchronizationTag::_whatever);
			}

			/* -------------------------------------------------------------------------- */
			template <class Entity>
			template <template <class> class Op, typename T>
			void SynchronizerImpl<Entity>::reduceSynchronizeArray(Array<T> & array) const {
			static_assert(std::is_same<Entity, Idx>::value,
			"Not implemented for other type than Idx");
			ReduceDataAccessor<Idx, Op, T> data_accessor(array,
			SynchronizationTag::_whatever);
			this->slaveReductionOnceImpl(data_accessor, SynchronizationTag::_whatever);
			this->synchronizeArray(array);
			}

			/* -------------------------------------------------------------------------- */
			} // namespace akantu

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