monofonIC/include/particle_generator.hh

// This file is part of monofonIC (MUSIC2)
// A software package to generate ICs for cosmological simulations
// Copyright (C) 2020 by Oliver Hahn
// 
// monofonIC is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// 
// monofonIC 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 General Public License for more details.
// 
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
#pragma once

#include <math/vec3.hh>
#include <grid_ghosts.hh>
#include <grid_interpolate.hh>

#if defined(USE_HDF5)
#include "HDF_IO.hh"
#endif

namespace particle
{
    using vec3 = std::array<real_t,3>;

    enum lattice
    {
        lattice_masked = -2, // masked lattices are SC lattices with a specifiable mask leaving out particles
        lattice_glass = -1,  // glass: needs a glass file
        lattice_sc = 0,  // SC : simple cubic
        lattice_bcc = 1, // BCC: body-centered cubic
        lattice_fcc = 2, // FCC: face-centered cubic
        lattice_rsc = 3, // RSC: refined simple cubic
    };

    const std::vector<std::vector<bool>> lattice_masks =
    {
        // mask from Richings et al. https://arxiv.org/pdf/2005.14495.pdf
        {true,true,true,true,true,true,true,false},
    };

    const std::vector<std::vector<vec3_t<real_t>>> lattice_shifts =
        {
            // first shift must always be zero! (otherwise set_positions and set_velocities break)
            /* SC : */ {{real_t{0.0}, real_t{0.0}, real_t{0.0}}},
            /* BCC: */ {{real_t{0.0}, real_t{0.0}, real_t{0.0}}, {real_t{0.5}, real_t{0.5}, real_t{0.5}}},
            /* FCC: */ {{real_t{0.0}, real_t{0.0}, real_t{0.0}}, {real_t{0.0}, real_t{0.5}, real_t{0.5}}, {real_t{0.5}, real_t{0.0}, real_t{0.5}}, {real_t{0.5}, real_t{0.5}, real_t{0.0}}},
            /* RSC: */ {{real_t{0.0}, real_t{0.0}, real_t{0.0}}, {real_t{0.0}, real_t{0.0}, real_t{0.5}}, {real_t{0.0}, real_t{0.5}, real_t{0.0}}, {real_t{0.0}, real_t{0.5}, real_t{0.5}}, {real_t{0.5}, real_t{0.0}, real_t{0.0}}, {real_t{0.5}, real_t{0.0}, real_t{0.5}}, {real_t{0.5}, real_t{0.5}, real_t{0.0}}, {real_t{0.5}, real_t{0.5}, real_t{0.5}}},
    };

    const std::vector<vec3_t<real_t>> second_lattice_shift =
        {
            /* SC : */ {real_t{0.5}, real_t{0.5}, real_t{0.5}}, // this corresponds to CsCl lattice
            /* BCC: */ {real_t{0.5}, real_t{0.5}, real_t{0.0}}, // is there a diatomic lattice with BCC base?!?
            /* FCC: */ {real_t{0.5}, real_t{0.5}, real_t{0.5}}, // this corresponds to NaCl lattice
                                        // /* FCC: */ {real_t{0.25}, real_t{0.25}, real_t{0.25}}, // this corresponds to Zincblende/GaAs lattice
            /* RSC: */ {real_t{0.25}, real_t{0.25}, real_t{0.25}},
    };

    template <typename field_t>
    class lattice_generator
    {
        protected:

        struct glass
        {
            using data_t = typename field_t::data_t;
            size_t num_p, off_p;
            grid_interpolate<1, field_t> interp_;
            std::vector<vec3> glass_posr;

            glass( config_file& cf, const field_t &field )
            : num_p(0), off_p(0), interp_( field )
            {
                std::vector<real_t> glass_pos;
                real_t lglassbox = 1.0;

                std::string glass_fname = cf.get_value<std::string>("setup", "GlassFileName");
                size_t ntiles = cf.get_value<size_t>("setup", "GlassTiles");

#if defined(USE_HDF5)
                HDFReadGroupAttribute(glass_fname, "Header", "BoxSize", lglassbox);
                HDFReadDataset(glass_fname, "/PartType1/Coordinates", glass_pos);
#else
                throw std::runtime_error("Class lattice requires HDF5 support. Enable and recompile.");
#endif

                size_t np_in_file = glass_pos.size() / 3;
#if defined(USE_MPI)
                num_p = np_in_file * ntiles * ntiles * ntiles / MPI::get_size();
                off_p = MPI::get_rank() * num_p;
#else
                num_p = np_in_file * ntiles * ntiles * ntiles;
                off_p = 0;
#endif

                music::ilog << "Glass file contains " << np_in_file << " particles." << std::endl;

                glass_posr.assign(num_p, {0.0, 0.0, 0.0});

                std::array<real_t, 3> ng({real_t(field.n_[0]), real_t(field.n_[1]), real_t(field.n_[2])});

                #pragma omp parallel for
                for (size_t i = 0; i < num_p; ++i)
                {
                    size_t idxpart = off_p + i;
                    size_t idx_in_glass = idxpart % np_in_file;
                    size_t idxtile = idxpart / np_in_file;
                    size_t tile_z = idxtile % (ntiles * ntiles);
                    size_t tile_y = ((idxtile - tile_z) / ntiles) % ntiles;
                    size_t tile_x = (((idxtile - tile_z) / ntiles) - tile_y) / ntiles;
                    glass_posr[i][0] = std::fmod((glass_pos[3 * idx_in_glass + 0] / lglassbox + real_t(tile_x)) / ntiles * ng[0] + ng[0], ng[0]);
                    glass_posr[i][1] = std::fmod((glass_pos[3 * idx_in_glass + 1] / lglassbox + real_t(tile_y)) / ntiles * ng[1] + ng[1], ng[1]);
                    glass_posr[i][2] = std::fmod((glass_pos[3 * idx_in_glass + 2] / lglassbox + real_t(tile_z)) / ntiles * ng[2] + ng[2], ng[2]);
                }

#if defined(USE_MPI)
                interp_.domain_decompose_pos(glass_posr);

                num_p = glass_posr.size();
                std::vector<size_t> all_num_p( MPI::get_size(), 0 );
                MPI_Allgather( &num_p, 1, MPI_UNSIGNED_LONG_LONG, &all_num_p[0], 1, MPI_UNSIGNED_LONG_LONG, MPI_COMM_WORLD );
                off_p = 0;
                for( int itask=0; itask<=MPI::get_rank(); ++itask ){
                    off_p += all_num_p[itask];
                }
#endif
            }

            void update_ghosts( const field_t &field )
            {
                interp_.update_ghosts( field );
            }

            data_t get_at( const vec3& x ) const noexcept
            {
                return interp_.get_cic_at( x );
            }

            size_t size() const noexcept
            {
                return num_p;
            }

            size_t offset() const noexcept
            {
                return off_p;
            }
        };

        std::unique_ptr<glass> glass_ptr_;

        private:
        particle::container particles_;
        size_t global_num_particles_;

        static constexpr int masksize_ = 2;
        std::array<int, masksize_*masksize_*masksize_> particle_type_mask_;

        inline int get_mask_value( const vec3_t<size_t>& global_idx_3d ) const
        {
            int sig = ((global_idx_3d[0]%masksize_)*masksize_
                       +global_idx_3d[1]%masksize_)*masksize_
                       +global_idx_3d[2]%masksize_;
            return particle_type_mask_[sig];
        }

        template< typename ggrid_t >
        inline real_t get_mean_mask_value( const ggrid_t& gg_field, const vec3_t<size_t>& global_idx_3d, size_t i, size_t j, size_t k, int lattice_index ) const
        {
            ptrdiff_t ox = (ptrdiff_t)i-(ptrdiff_t)(global_idx_3d[0]%masksize_);
            ptrdiff_t oy = (ptrdiff_t)j-(ptrdiff_t)(global_idx_3d[1]%masksize_);
            ptrdiff_t oz = (ptrdiff_t)k-(ptrdiff_t)(global_idx_3d[2]%masksize_);
            size_t count_full{0}, count_masked{0};
            real_t mean_full{0.0}, mean_masked{0.0};
            for( size_t i=0; i<masksize_; ++i ){
                for( size_t j=0; j<masksize_; ++j ){
                    for( size_t k=0; k<masksize_; ++k ){
                        mean_full += gg_field.relem( ox+i, oy+j, oz+k );
                        ++count_full;
                        if( particle_type_mask_[4*i+2*j+k] == lattice_index ){
                            mean_masked += gg_field.relem( ox+i, oy+j, oz+k );
                            ++count_masked;
                        }
                    }
                }
            }
            mean_full /= count_full;
            mean_masked /= count_masked;
            return mean_masked - mean_full;
        }

        public:
        /**
         * @brief Construct a new lattice generator object
         * 
         * @param lattice_type Type of the lattice (currently: 0=SC, 1=BCC, 2=FCC, 3=double SC, -1=glass, -2=masked SC)
         * @param lattice_index Index of the 'atom type', i.e. whether CDM, baryons, ... (currently only supports 0 or 1)
         * @param b64reals Boolean whether 64bit floating point shall be used to store positions/velocities/masses
         * @param b64ids  Boolean whether 64bit integers should be used for IDS
         * @param bwithmasses Boolean whether distinct masses for each particle shall be stored
         * @param IDoffset The global ID offset to be applied to this generation of particles
         * @param field Reference to the field from which particles shall be generated (used only to set dimensions)
         * @param cf Reference to the config_file object
         */

        lattice_generator(lattice lattice_type, int lattice_index, const bool b64reals, const bool b64ids, const bool bwithmasses, size_t IDoffset, const field_t &field, config_file &cf)
        : global_num_particles_(0)
        {
            // initialise the particle mask with zeros (only used if lattice_type==lattice_masked)
            for( auto& m : particle_type_mask_) m = 0;

            if (lattice_type >= 0) // These are the Bravais lattices
            {
                music::wlog << "Glass ICs will currently be incorrect due to disabled ghost zone updates! ";

                // number of modes present in the field
                const size_t num_p_in_load = field.local_size();
                // unless SC lattice is used, particle number is a multiple of the number of modes (=num_p_in_load):
                const size_t overload = 1ull << std::max<int>(0, lattice_type); // 1 for sc, 2 for bcc, 4 for fcc, 8 for rsc
                // allocate memory for all local particles
                particles_.allocate(overload * num_p_in_load, b64reals, b64ids, bwithmasses);
                // set the global number of particles for this lattice_type and lattice_index
                global_num_particles_ = field.global_size() * overload;

                // set particle IDs to the Lagrangian coordinate (1D encoded) with additionally the field shift encoded as well

                IDoffset = IDoffset * overload * field.global_size();

                for (size_t i = 0, ipcount = 0; i < field.rsize(0); ++i)
                {
                    for (size_t j = 0; j < field.rsize(1); ++j)
                    {
                        for (size_t k = 0; k < field.rsize(2); ++k, ++ipcount)
                        {
                            for (size_t iload = 0; iload < overload; ++iload)
                            {
                                if (b64ids)
                                {
                                    particles_.set_id64(ipcount + iload * num_p_in_load, IDoffset + overload * field.get_cell_idx_1d(i, j, k) + iload);
                                }
                                else
                                {
                                    particles_.set_id32(ipcount + iload * num_p_in_load, IDoffset + overload * field.get_cell_idx_1d(i, j, k) + iload);
                                }
                            }
                        }
                    }
                }
            }
            else if( lattice_type == lattice_masked )
            {
                if( field.global_size()%8 != 0 ){
                    music::elog << "For masked lattice type, linear field resolution must be a multiple of two." << std::endl;
                    abort();
                }

                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For masked lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                // set the particle mask 
                if( cf.get_value_safe("setup","DoBaryons",false) )
                {
                    // mask everywehere 0, except the last element
                    for( auto& m : particle_type_mask_) m = 0;
                    particle_type_mask_[7] = 1;
                }else{
                    // mask everywehere 0
                    for( auto& m : particle_type_mask_) m = 0;
                }

                // count number of particles taking into account masking
                size_t ipcount = 0;
                for (size_t i = 0; i < field.rsize(0); ++i)
                {
                    for (size_t j = 0; j < field.rsize(1); ++j)
                    {
                        for (size_t k = 0; k < field.rsize(2); ++k)
                        {
                            if( this->get_mask_value(field.get_cell_idx_3d(i,j,k)) != lattice_index ) continue;
                            ++ipcount;
                        }
                    }
                }

                // set global number of particles
#if defined(USE_MPI)
                MPI_Allreduce( &ipcount, &global_num_particles_, 1, MPI_UNSIGNED_LONG_LONG, MPI_SUM, MPI_COMM_WORLD );
#else
                global_num_particles_ = ipcount;
#endif

                // number of modes present in the field
                const size_t num_p_in_load = ipcount;

                // allocate memory for all local particles
                particles_.allocate(num_p_in_load, b64reals, b64ids, bwithmasses);

                // set particle IDs to the Lagrangian coordinate (1D encoded) with additionally the field shift encoded as well
                IDoffset = IDoffset * field.global_size();

                for (size_t i = 0, ipcount = 0; i < field.rsize(0); ++i)
                {
                    for (size_t j = 0; j < field.rsize(1); ++j)
                    {
                        for (size_t k = 0; k < field.rsize(2); ++k)
                        {
                            if( this->get_mask_value(field.get_cell_idx_3d(i,j,k)) != lattice_index ) continue;

                            if (b64ids)
                            {
                                particles_.set_id64(ipcount, IDoffset + field.get_cell_idx_1d(i, j, k));
                            }
                            else
                            {
                                particles_.set_id32(ipcount, IDoffset + field.get_cell_idx_1d(i, j, k));
                            }
                            ++ipcount;
                        }
                    }
                }

            }
            else if( lattice_type == lattice_glass )
            {
                glass_ptr_ = std::make_unique<glass>( cf, field );
                particles_.allocate(glass_ptr_->size(), b64reals, b64ids, false);

                #pragma omp parallel for
                for (size_t i = 0; i < glass_ptr_->size(); ++i)
                {
                    if (b64ids)
                    {
                        particles_.set_id64(i, IDoffset + i + glass_ptr_->offset());
                    }
                    else
                    {
                        particles_.set_id32(i, IDoffset + i + glass_ptr_->offset());
                    }
                }
            }

            music::ilog << "Created Particles [" << lattice_index << "] : " << global_num_particles_ << std::endl;

        }

        // invalidates field, phase shifted to unspecified position after return
        void set_masses(const lattice lattice_type, int lattice_index, const real_t munit, const bool b64reals, field_t &field, config_file &cf)
        {
            // works only for Bravais types and masked type
            assert( lattice_type>=0 || lattice_type==lattice_masked );

            if (lattice_type >= 0) // Bravais lattices
            {
                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For Bravais lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                const size_t overload = 1ull << std::max<int>(0, lattice_type); // 1 for sc, 2 for bcc, 4 for fcc, 8 for rsc
                const size_t num_p_in_load = field.local_size();
                const real_t pmeanmass = munit / real_t(field.global_size()* overload);

                bool bmass_negative = false;
                auto mean_pm = field.mean() * pmeanmass;
                auto std_pm  = field.std()  * pmeanmass;

                for (int ishift = 0; ishift < (1 << lattice_type); ++ishift)
                {
                    // if we are dealing with the secondary lattice, apply a global shift
                    if (ishift == 0 && lattice_index > 0)
                    {
                        field.shift_field(second_lattice_shift[lattice_type]);
                    }

                    // can omit first shift since zero by convention, unless shifted already above, otherwise apply relative phase shift
                    if (ishift > 0)
                    {
                        field.shift_field(lattice_shifts[lattice_type][ishift] - lattice_shifts[lattice_type][ishift - 1]);
                    }
                    // read out values from phase shifted field and set assoc. particle's value
                    const auto ipcount0 = ishift * num_p_in_load;
                    for (size_t i = 0, ipcount = ipcount0; i < field.size(0); ++i)
                    {
                        for (size_t j = 0; j < field.size(1); ++j)
                        {
                            for (size_t k = 0; k < field.size(2); ++k)
                            {
                                // get
                                const auto pmass = pmeanmass * field.relem(i, j, k);

                                // check for negative mass
                                bmass_negative |= pmass<0.0;

                                // set
                                if (b64reals) particles_.set_mass64(ipcount++, pmass);
                                else particles_.set_mass32(ipcount++, pmass);
                            }
                        }
                    }
                }
                
                // diagnostics
                music::ilog << "Particle Mass :  mean/munit = " << mean_pm/munit  << " ; fractional RMS = " << std_pm / mean_pm * 100.0 << "%" << std::endl;
                if(std_pm / mean_pm > 0.1 ) music::wlog << "Particle mass perturbation larger than 10%, consider decreasing \n\t  the starting redshift or disabling baryon decaying modes." << std::endl;
                if(bmass_negative) music::elog << "Negative particle mass produced! Decrease the starting \n\t  redshift or disable baryon decaying modes!" << std::endl;
            } else if( lattice_type == lattice_masked ) {
                if( field.global_size()%8 != 0 ){
                    music::elog << "For masked lattice type, linear field resolution must be a multiple of two." << std::endl;
                    abort();
                }

                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For masked lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                grid_with_ghosts<1, true, true, field_t> gg_field(field);

                const real_t pmeanmass = munit / global_num_particles_;

                bool bmass_negative = false;
                real_t mean_pm = 0.0;//field.mean() * pmeanmass;
                real_t std_pm  = 0.0; //field.std()  * pmeanmass;

                // read out values from phase shifted field and set assoc. particle's value
                for (size_t i = 0, ipcount = 0; i < field.size(0); ++i)
                {
                    for (size_t j = 0; j < field.size(1); ++j)
                    {
                        for (size_t k = 0; k < field.size(2); ++k)
                        {
                            const auto idx3 = field.get_cell_idx_3d(i,j,k);

                            if( this->get_mask_value(idx3) != lattice_index ) continue;

                            const auto mean_mask = this->get_mean_mask_value( gg_field, idx3, i, j, k, lattice_index );

                            // get
                            const auto pmass = pmeanmass * (field.relem(i, j, k) - mean_mask);

                            // check for negative mass
                            bmass_negative |= pmass<0.0;

                            // set
                            if (b64reals) particles_.set_mass64(ipcount++, pmass);
                            else particles_.set_mass32(ipcount++, pmass);

                            // statistics
                            mean_pm += pmass;
                            std_pm += pmass*pmass;
                        }
                    }
                }
                #if defined(USE_MPI)
                {
                    double local_mean_pm = mean_pm, local_std_pm = std_pm;
                    MPI_Allreduce( &local_mean_pm, &mean_pm, 1, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD );
                    MPI_Allreduce( &local_std_pm, &std_pm, 1, MPI_DOUBLE, MPI_SUM, MPI_COMM_WORLD );
                }
                #endif
                mean_pm /= global_num_particles_;
                std_pm /= global_num_particles_;
                std_pm -= mean_pm*mean_pm;
                
                // diagnostics
                music::ilog << "Particle Mass :  mean/munit = " << mean_pm/munit  << " ; fractional RMS = " << std_pm / mean_pm * 100.0 << "%" << std::endl;
                if(std_pm / mean_pm > 0.1 ) music::wlog << "Particle mass perturbation larger than 10%, consider decreasing \n\t  the starting redshift or disabling baryon decaying modes." << std::endl;
                if(bmass_negative) music::elog << "Negative particle mass produced! Decrease the starting \n\t  redshift or disable baryon decaying modes!" << std::endl;
            }else{
                // should not happen
                music::elog << "Cannot have individual particle masses for glasses!" << std::endl;
                throw std::runtime_error("cannot have individual particle masses for glasses");
            }
        }

        // invalidates field, phase shifted to unspecified position after return
        void set_positions(const lattice lattice_type, int lattice_index, int idim, real_t lunit, const bool b64reals, field_t &field, config_file &cf)
        {
            
            if (lattice_type >= 0) // Bravais lattice
            {
                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For Bravais lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                const size_t num_p_in_load = field.local_size();
                for (int ishift = 0; ishift < (1 << lattice_type); ++ishift)
                {
                    // if we are dealing with the secondary lattice, apply a global shift
                    if (ishift == 0 && lattice_index==1)
                    {
                        field.shift_field(second_lattice_shift[lattice_type]);
                    }

                    // can omit first shift since zero by convention, unless shifted already above, otherwise apply relative phase shift
                    if (ishift > 0)
                    {
                        field.shift_field(lattice_shifts[lattice_type][ishift] - lattice_shifts[lattice_type][ishift - 1]);
                    }
                    // read out values from phase shifted field and set assoc. particle's value
                    const auto ipcount0 = ishift * num_p_in_load;
                    for (size_t i = 0, ipcount = ipcount0; i < field.size(0); ++i)
                    {
                        for (size_t j = 0; j < field.size(1); ++j)
                        {
                            for (size_t k = 0; k < field.size(2); ++k)
                            {
                                auto pos = field.template get_unit_r_shifted<real_t>(i, j, k, lattice_shifts[lattice_type][ishift] + (lattice_index==1 ? second_lattice_shift[lattice_type] : vec3_t<real_t>{real_t(0.), real_t(0.), real_t(0.)}));
                                if (b64reals)
                                {
                                    particles_.set_pos64(ipcount++, idim, pos[idim] * lunit + field.relem(i, j, k));
                                }
                                else
                                {
                                    particles_.set_pos32(ipcount++, idim, pos[idim] * lunit + field.relem(i, j, k));
                                }
                            }
                        }
                    }
                }
            }
            else if( lattice_type == lattice_masked ) 
            {
                if( field.global_size()%8 != 0 ){
                    music::elog << "For masked lattice type, linear field resolution must be a multiple of two." << std::endl;
                    abort();
                }

                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For masked lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                for (size_t i = 0, ipcount = 0; i < field.size(0); ++i)
                {
                    for (size_t j = 0; j < field.size(1); ++j)
                    {
                        for (size_t k = 0; k < field.size(2); ++k)
                        {
                            if( this->get_mask_value(field.get_cell_idx_3d(i,j,k)) != lattice_index ) continue;

                            // get position (in box units) of the current cell of 3d array 'field'
                            auto pos = field.template get_unit_r<real_t>(i, j, k);
                            // add the displacement to get the particle position
                            if (b64reals){
                                particles_.set_pos64(ipcount++, idim, pos[idim] * lunit + field.relem(i, j, k));
                            }else{
                                particles_.set_pos32(ipcount++, idim, pos[idim] * lunit + field.relem(i, j, k));
                            }
                        }
                    }
                }
            }
            else
            {
                glass_ptr_->update_ghosts( field );
                #pragma omp parallel for
                for (size_t i = 0; i < glass_ptr_->size(); ++i)
                {
                    auto pos = glass_ptr_->glass_posr[i];
                    real_t disp = glass_ptr_->get_at(pos);
                    if (b64reals)
                    {
                        particles_.set_pos64(i, idim, pos[idim] / field.n_[idim] * lunit + disp);
                    }
                    else
                    {
                        particles_.set_pos32(i, idim, pos[idim] / field.n_[idim] * lunit + disp);
                    }
                }
            }
        }

        void set_velocities(lattice lattice_type, int lattice_index, int idim, const bool b64reals, field_t &field, config_file &cf)
        {
            if (lattice_type >= 0) // Bravais lattice
            {
                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For Bravais lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                const size_t num_p_in_load = field.local_size();
                for (int ishift = 0; ishift < (1 << lattice_type); ++ishift)
                {
                    // if we are dealing with the secondary lattice, apply a global shift
                    if (ishift == 0 && lattice_index==1)
                    {
                        field.shift_field(second_lattice_shift[lattice_type]);
                    }
                    // can omit first shift since zero by convention, unless shifted already above, otherwise apply relative phase shift
                    if (ishift > 0)
                    {
                        field.shift_field(lattice_shifts[lattice_type][ishift] - lattice_shifts[lattice_type][ishift - 1]);
                    }
                    // read out values from phase shifted field and set assoc. particle's value
                    const auto ipcount0 = ishift * num_p_in_load;
                    for (size_t i = 0, ipcount = ipcount0; i < field.size(0); ++i)
                    {
                        for (size_t j = 0; j < field.size(1); ++j)
                        {
                            for (size_t k = 0; k < field.size(2); ++k)
                            {
                                if (b64reals)
                                {
                                    particles_.set_vel64(ipcount++, idim, field.relem(i, j, k));
                                }
                                else
                                {
                                    particles_.set_vel32(ipcount++, idim, field.relem(i, j, k));
                                }
                            }
                        }
                    }
                }
            }
            else if( lattice_type == lattice_masked ) 
            {
                if( field.global_size()%8 != 0 ){
                    music::elog << "For masked lattice type, linear field resolution must be a multiple of two." << std::endl;
                    abort();
                }

                if( lattice_index > 1 || lattice_index < 0 ){
                    music::elog << "For masked lattice type, lattice index must be 0 or 1." << std::endl;
                    abort();
                }

                for (size_t i = 0, ipcount = 0; i < field.size(0); ++i)
                {
                    for (size_t j = 0; j < field.size(1); ++j)
                    {
                        for (size_t k = 0; k < field.size(2); ++k)
                        {
                            if( this->get_mask_value(field.get_cell_idx_3d(i,j,k)) != lattice_index ) continue;

                            if (b64reals){
                                particles_.set_vel64(ipcount++, idim, field.relem(i, j, k));
                            }else{
                                particles_.set_vel32(ipcount++, idim, field.relem(i, j, k));
                            }
                        }
                    }
                }
            }
            else
            {
                glass_ptr_->update_ghosts( field );
                #pragma omp parallel for
                for (size_t i = 0; i < glass_ptr_->size(); ++i)
                {
                    auto pos = glass_ptr_->glass_posr[i];
                    real_t vel = glass_ptr_->get_at(pos);
                    if (b64reals)
                    {
                        particles_.set_vel64(i, idim, vel);
                    }
                    else
                    {
                        particles_.set_vel32(i, idim, vel);
                    }
                }
            }
        }

        const particle::container& get_particles() const noexcept{
            return particles_;
        }

    }; // struct lattice

} // namespace particle