InjectorMomentum.H

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/* Copyright 2019-2020 Andrew Myers, Axel Huebl, Cameron Yang,
 * Maxence Thevenet, Weiqun Zhang
 *
 * This file is part of WarpX.
 *
 * License: BSD-3-Clause-LBNL
 */
#ifndef WARPX_INJECTOR_MOMENTUM_H_
#define WARPX_INJECTOR_MOMENTUM_H_
 
#include "GetTemperature.H"
#include "GetVelocity.H"
#include "TemperatureProperties.H"
#include "VelocityProperties.H"
#include "SampleGaussianFluxDistribution.H"
#include "Utils/TextMsg.H"
#include "Utils/WarpXConst.H"
 
#include <AMReX.H>
#include <AMReX_Config.H>
#include <AMReX_Dim3.H>
#include <AMReX_GpuQualifiers.H>
#include <AMReX_REAL.H>
#include <AMReX_Parser.H>
#include <AMReX_Random.H>
 
#include <AMReX_BaseFwd.H>
 
#include <cmath>
#include <string>
 
// struct whose getMomentum returns constant momentum.
struct InjectorMomentumConstant
{
    InjectorMomentumConstant (amrex::Real a_ux, amrex::Real a_uy, amrex::Real a_uz) noexcept
        : m_ux(a_ux), m_uy(a_uy), m_uz(a_uz) {}
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real, amrex::Real, amrex::Real,
                 amrex::RandomEngine const&) const noexcept
    {
        return amrex::XDim3{m_ux,m_uy,m_uz};
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real, amrex::Real, amrex::Real) const noexcept
    {
        return amrex::XDim3{m_ux,m_uy,m_uz};
    }
 
private:
    amrex::Real m_ux, m_uy, m_uz;
};
 
// struct whose getMomentum returns momentum for 1 particle, from random
// gaussian distribution.
struct InjectorMomentumGaussian
{
    InjectorMomentumGaussian (amrex::Real a_ux_m, amrex::Real a_uy_m,
                              amrex::Real a_uz_m, amrex::Real a_ux_th,
                              amrex::Real a_uy_th, amrex::Real a_uz_th) noexcept
        : m_ux_m(a_ux_m), m_uy_m(a_uy_m), m_uz_m(a_uz_m),
          m_ux_th(a_ux_th), m_uy_th(a_uy_th), m_uz_th(a_uz_th)
        {}
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real /*x*/, amrex::Real /*y*/, amrex::Real /*z*/,
                 amrex::RandomEngine const& engine) const noexcept
    {
        return amrex::XDim3{amrex::RandomNormal(m_ux_m, m_ux_th, engine),
                            amrex::RandomNormal(m_uy_m, m_uy_th, engine),
                            amrex::RandomNormal(m_uz_m, m_uz_th, engine)};
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real /*x*/, amrex::Real /*y*/, amrex::Real /*z*/) const noexcept
    {
        return amrex::XDim3{m_ux_m, m_uy_m, m_uz_m};
    }
 
private:
    amrex::Real m_ux_m, m_uy_m, m_uz_m;
    amrex::Real m_ux_th, m_uy_th, m_uz_th;
};
 
// struct whose getMomentum returns momentum for 1 particle, from random
// gaussian flux distribution in the specified direction.
// Along the normal axis, the distribution is v*Gaussian,
// with the sign set by flux_direction.
struct InjectorMomentumGaussianFlux
{
    InjectorMomentumGaussianFlux (amrex::Real a_ux_m, amrex::Real a_uy_m,
                                  amrex::Real a_uz_m, amrex::Real a_ux_th,
                                  amrex::Real a_uy_th, amrex::Real a_uz_th,
                                  int a_flux_normal_axis, int a_flux_direction) noexcept
        : m_ux_m(a_ux_m), m_uy_m(a_uy_m), m_uz_m(a_uz_m),
          m_ux_th(a_ux_th), m_uy_th(a_uy_th), m_uz_th(a_uz_th),
          m_flux_normal_axis(a_flux_normal_axis),
          m_flux_direction(a_flux_direction)
    {
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real /*x*/, amrex::Real /*y*/, amrex::Real /*z*/,
                 amrex::RandomEngine const& engine) const noexcept
    {
        using namespace amrex::literals;
 
        // Generate the distribution in the direction of the flux
        amrex::Real u_m = 0, u_th = 0;
        if (m_flux_normal_axis == 0) {
            u_m = m_ux_m;
            u_th = m_ux_th;
        } else if (m_flux_normal_axis == 1) {
            u_m = m_uy_m;
            u_th = m_uy_th;
        } else if (m_flux_normal_axis == 2) {
            u_m = m_uz_m;
            u_th = m_uz_th;
        }
        amrex::Real u = generateGaussianFluxDist(u_m, u_th, engine);
        if (m_flux_direction < 0) { u = -u; }
 
        // Note: Here, in RZ geometry, the variables `ux` and `uy` actually
        // correspond to the radial and azimuthal component of the momentum
        // (and e.g.`m_flux_normal_axis==1` corresponds to v*Gaussian along theta)
        amrex::Real const ux = (m_flux_normal_axis == 0 ? u : amrex::RandomNormal(m_ux_m, m_ux_th, engine));
        amrex::Real const uy = (m_flux_normal_axis == 1 ? u : amrex::RandomNormal(m_uy_m, m_uy_th, engine));
        amrex::Real const uz = (m_flux_normal_axis == 2 ? u : amrex::RandomNormal(m_uz_m, m_uz_th, engine));
        return amrex::XDim3{ux, uy, uz};
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real /*x*/, amrex::Real /*y*/, amrex::Real /*z*/) const noexcept
    {
        return amrex::XDim3{m_ux_m, m_uy_m, m_uz_m};
    }
 
private:
    amrex::Real m_ux_m, m_uy_m, m_uz_m;
    amrex::Real m_ux_th, m_uy_th, m_uz_th;
    int m_flux_normal_axis;
    int m_flux_direction;
};
 
 
// struct whose getMomentum returns momentum for 1 particle, from random
// uniform distribution u_min < u < u_max
struct InjectorMomentumUniform
{
    InjectorMomentumUniform (amrex::Real a_ux_min, amrex::Real a_uy_min,
                              amrex::Real a_uz_min, amrex::Real a_ux_max,
                              amrex::Real a_uy_max, amrex::Real a_uz_max) noexcept
        : m_ux_min(a_ux_min), m_uy_min(a_uy_min), m_uz_min(a_uz_min),
          m_ux_max(a_ux_max), m_uy_max(a_uy_max), m_uz_max(a_uz_max),
          m_Dux(m_ux_max - m_ux_min),
          m_Duy(m_uy_max - m_uy_min),
          m_Duz(m_uz_max - m_uz_min),
          m_ux_h(amrex::Real(0.5) * (m_ux_max + m_ux_min)),
          m_uy_h(amrex::Real(0.5) * (m_uy_max + m_uy_min)),
          m_uz_h(amrex::Real(0.5) * (m_uz_max + m_uz_min))
        {}
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real /*x*/, amrex::Real /*y*/, amrex::Real /*z*/,
                 amrex::RandomEngine const& engine) const noexcept
    {
        return amrex::XDim3{m_ux_min + amrex::Random(engine) * m_Dux,
                            m_uy_min + amrex::Random(engine) * m_Duy,
                            m_uz_min + amrex::Random(engine) * m_Duz};
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real /*x*/, amrex::Real /*y*/, amrex::Real /*z*/) const noexcept
    {
        return amrex::XDim3{m_ux_h, m_uy_h, m_uz_h};
    }
 
private:
    amrex::Real m_ux_min, m_uy_min, m_uz_min;
    amrex::Real m_ux_max, m_uy_max, m_uz_max;
    amrex::Real m_Dux, m_Duy, m_Duz;
    amrex::Real m_ux_h, m_uy_h, m_uz_h;
};
 
// struct whose getMomentum returns momentum for 1 particle with relativistic
// bulk drift momentum u_mean, from the Maxwellian distribution.
struct InjectorMomentumMaxwellian
{
    // Constructor whose inputs are:
    // a reference to the initial temperature container t,
    // a reference to the initial velocity container b
    InjectorMomentumMaxwellian(GetTemperatureVector const& t, GetVelocityVector const& b) noexcept
        : velocity(b), temperature(t)
        {}
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real const x, amrex::Real const y, amrex::Real const z,
                 amrex::RandomEngine const& engine) const noexcept
    {
        using namespace amrex::literals;
        const amrex::XDim3 u_std = temperature(x,y,z);
        const amrex::XDim3 u_mean = velocity(x,y,z);
        if (u_std.x < 0.0_rt || u_std.y < 0.0_rt || u_std.z < 0.0_rt) {
            amrex::Abort("The standard deviation of normalized momentum must be non-negative.");
        }
        const amrex::Real ux_std = amrex::RandomNormal(u_mean.x, u_std.x, engine);
        const amrex::Real uy_std = amrex::RandomNormal(u_mean.y, u_std.y, engine);
        const amrex::Real uz_std = amrex::RandomNormal(u_mean.z, u_std.z, engine);
        return amrex::XDim3 {ux_std, uy_std, uz_std};
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real const x, amrex::Real const y, amrex::Real const z) const noexcept
    {
        using namespace amrex::literals;
        const amrex::XDim3 u_mean = velocity(x,y,z);
        return amrex::XDim3 {u_mean.x, u_mean.y, u_mean.z};
    }
 
private:
    GetVelocityVector velocity;
    GetTemperatureVector temperature;
};
 
// struct whose getMomentum returns momentum for 1 particle with relativistic
// drift velocity beta, from the Maxwell-Juttner distribution. Method is from
// Zenitani 2015 (Phys. Plasmas 22, 042116).
struct InjectorMomentumJuttner
{
    // Constructor whose inputs are:
    // a reference to the initial temperature container t,
    // a reference to the initial velocity container b
    InjectorMomentumJuttner(GetTemperature const& t, GetVelocity const& b) noexcept
        : velocity(b), temperature(t)
        {}
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real const x, amrex::Real const y, amrex::Real const z,
                 amrex::RandomEngine const& engine) const noexcept
    {
        using namespace amrex::literals;
        amrex::Real x1, x2, gamma;
        amrex::Real u [3];
        amrex::Real const theta = temperature(x,y,z);
        if (theta < 0) {
            amrex::Abort("Temperature parameter theta is less than zero, "
                "which is not allowed for Maxwell-Juttner distribution.");
        }
        // Calculate local velocity and abort if |beta|>=1
        amrex::Real const beta = velocity(x,y,z);
        if (beta <= -1._rt || beta >= 1._rt) {
            amrex::Abort("beta = v/c magnitude greater than or equal to 1");
        }
        int const dir = velocity.direction();
        // The Sobol rejection method used below becomes inefficient at low
        // temperature: its acceptance efficiency is K_2(1/theta)/(2 theta^2),
        // which tends to zero as theta -> 0
        // (Zenitani et al. Phys. Plasmas 22, 042116, 2015, Eq. 13).
        // For theta < 0.1 the Maxwell-Juttner distribution is indistinguishable
        // from a non-relativistic Maxwellian, so we instead sample the
        // momentum from a Gaussian with thermal spread
        // u_th = sqrt(theta) per component (i.e. sqrt(kB*T/(m*c^2)),
        // in the Lorentz frame that moves with the bulk drift
        // where u is the normalized momentum u=gamma*beta.
        // The flipping method and Lorentz transform below then handle
        // the bulk drift, exactly as for the Sobol-sampled momentum.
        if (theta < 0.1_rt) {
            amrex::Real const u_th = std::sqrt(theta);
            u[0] = amrex::RandomNormal(0._rt, u_th, engine);
            u[1] = amrex::RandomNormal(0._rt, u_th, engine);
            u[2] = amrex::RandomNormal(0._rt, u_th, engine);
            gamma = std::sqrt(1._rt + u[0]*u[0] + u[1]*u[1] + u[2]*u[2]);
        } else {
            // Sobol method for sampling MJ Speeds,
            // from Zenitani et al. Phys. Plasmas 22, 042116, 2015, Eq. 13.
            x1 = 0._rt;
            gamma = 0._rt;
            u[dir] = 0._rt;
            // This condition is equation 10 in Zenitani,
            // though x1 is defined differently.
            while(u[dir]-gamma <= x1)
            {
                u[dir] = -theta*
                    std::log(amrex::Random(engine)*amrex::Random(engine)*amrex::Random(engine));
                gamma = std::sqrt(1._rt+u[dir]*u[dir]);
                x1 = theta*std::log(amrex::Random(engine));
            }
            // The following code samples a random unit vector
            // and multiplies the result by speed u[dir].
            x1 = amrex::Random(engine);
            x2 = amrex::Random(engine);
            // Direction dir is an input parameter that sets the boost direction:
            // 'x' -> d = 0, 'y' -> d = 1, 'z' -> d = 2.
            auto const [sin_x2, cos_x2] = amrex::Math::sincos(2._rt*MathConst::pi*x2);
            u[(dir+1)%3] = 2._rt*u[dir]*std::sqrt(x1*(1._rt-x1))*sin_x2;
            u[(dir+2)%3] = 2._rt*u[dir]*std::sqrt(x1*(1._rt-x1))*cos_x2;
            // The value of dir is the boost direction to be transformed.
            u[dir] = u[dir]*(2._rt*x1-1._rt);
        }
        x1 = amrex::Random(engine);
        // The following condition is equation 32 in Zenitani, called
        // The flipping method. It transforms the integral: d3x' -> d3x
        // where d3x' is the volume element for positions in the boosted frame.
        // The particle positions and densities can be initialized in the
        // simulation frame with this method.
        // The flipping method can similarly transform any
        // symmetric distribution from one reference frame to another moving at
        // a relative velocity of beta.
        // An equivalent alternative to this method native to WarpX
        // would be to initialize the particle positions and densities in the
        // frame moving at speed beta, and then perform a Lorentz transform
        // on their positions and MJ sampled velocities to the simulation frame.
        if(-beta*u[dir]/gamma>x1)
        {
            u[dir] = -u[dir];
        }
        // This Lorentz transform is equation 17 in Zenitani.
        // It transforms the integral d3u' -> d3u
        // where d3u' is the volume element for momentum in the boosted frame.
        u[dir] = 1._rt/std::sqrt(1._rt-beta*beta)*(u[dir]+gamma*beta);
        // Note that if beta = 0 then the flipping method and Lorentz transform
        // have no effect on the u[dir] direction.
        return amrex::XDim3 {u[0],u[1],u[2]};
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real const x, amrex::Real const y, amrex::Real const z) const noexcept
    {
        using namespace amrex::literals;
        amrex::Real u[3];
        for (auto& el : u) { el = 0.0_rt; }
        amrex::Real const beta = velocity(x,y,z);
        int const dir = velocity.direction();
        auto const gamma = 1._rt/std::sqrt(1._rt-beta*beta);
        u[dir] = gamma*beta;
        return amrex::XDim3 {u[0],u[1],u[2]};
    }
 
private:
    GetVelocity velocity;
    GetTemperature temperature;
};
 
// struct whose getMomentum returns local momentum computed from parser.
struct InjectorMomentumParser
{
    explicit InjectorMomentumParser (GetVelocityVector const& a_velocity) noexcept
        : m_velocity(a_velocity) {}
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real x, amrex::Real y, amrex::Real z,
                 amrex::RandomEngine const&) const noexcept
    {
        return m_velocity(x,y,z);
    }
 
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real x, amrex::Real y, amrex::Real z) const noexcept
    {
        return m_velocity(x,y,z);
    }
 
    GetVelocityVector m_velocity;
};
 
// Base struct for momentum injector.
// InjectorMomentum contains a union (called Object) that holds any one
// instance of:
// - InjectorMomentumConstant       : to generate constant density;
// - InjectorMomentumGaussian       : to generate gaussian distribution;
// - InjectorMomentumGaussianFlux   : to generate v*gaussian distribution;
// - InjectorMomentumParser         : to generate momentum from parser;
// - InjectorMomentumMaxwellian     : to generate Maxwellian distribution;
// The choice is made at runtime, depending in the constructor called.
// This mimics virtual functions.
struct InjectorMomentum
{
    // This constructor stores a InjectorMomentumConstant in union object.
    InjectorMomentum (InjectorMomentumConstant* t,
                      amrex::Real a_ux, amrex::Real a_uy, amrex::Real a_uz)
        : type(Type::constant),
          object(t, a_ux, a_uy, a_uz)
    { }
 
    // This constructor stores a InjectorMomentumParser in union object.
    InjectorMomentum (InjectorMomentumParser* t,
                      GetVelocityVector const& a_velocity)
        : type(Type::parser),
          object(t, a_velocity)
    { }
 
    // This constructor stores a InjectorMomentumGaussian in union object.
    InjectorMomentum (InjectorMomentumGaussian* t,
                      amrex::Real a_ux_m, amrex::Real a_uy_m, amrex::Real a_uz_m,
                      amrex::Real a_ux_th, amrex::Real a_uy_th, amrex::Real a_uz_th)
        : type(Type::gaussian),
          object(t,a_ux_m,a_uy_m,a_uz_m,a_ux_th,a_uy_th,a_uz_th)
    { }
 
    // This constructor stores a InjectorMomentumGaussianFlux in union object.
    InjectorMomentum (InjectorMomentumGaussianFlux* t,
                      amrex::Real a_ux_m, amrex::Real a_uy_m, amrex::Real a_uz_m,
                      amrex::Real a_ux_th, amrex::Real a_uy_th, amrex::Real a_uz_th,
                      int a_flux_normal_axis, int a_flux_direction)
        : type(Type::gaussianflux),
          object(t,a_ux_m,a_uy_m,a_uz_m,a_ux_th,a_uy_th,a_uz_th,a_flux_normal_axis,a_flux_direction)
    { }
 
    // This constructor stores a InjectorMomentumUniform in union object.
    InjectorMomentum (InjectorMomentumUniform* t,
                      amrex::Real a_ux_min, amrex::Real a_uy_min, amrex::Real a_uz_min,
                      amrex::Real a_ux_max, amrex::Real a_uy_max, amrex::Real a_uz_max)
        : type(Type::uniform),
          object(t,a_ux_min,a_uy_min,a_uz_min,a_ux_max,a_uy_max,a_uz_max)
    { }
 
    InjectorMomentum (InjectorMomentumMaxwellian* t,
                       GetTemperatureVector const& temperature, GetVelocityVector const& velocity)
         : type(Type::maxwellian),
           object(t, temperature, velocity)
    { }
 
    // This constructor stores a InjectorMomentumJuttner in union object.
    InjectorMomentum (InjectorMomentumJuttner* t,
                      GetTemperature const& temperature, GetVelocity const& velocity)
         : type(Type::juttner),
           object(t, temperature, velocity)
    { }
 
    // Explicitly prevent the compiler from generating copy constructors
    // and copy assignment operators.
    InjectorMomentum (InjectorMomentum const&) = delete;
    InjectorMomentum (InjectorMomentum&&) = delete;
    void operator= (InjectorMomentum const&) = delete;
    void operator= (InjectorMomentum &&) = delete;
 
    // Default destructor
    ~InjectorMomentum() = default;
 
    void clear ();
 
    // call getMomentum from the object stored in the union
    // (the union is called Object, and the instance is called object).
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getMomentum (amrex::Real x, amrex::Real y, amrex::Real z,
                 amrex::RandomEngine const& engine) const noexcept
    {
        switch (type)
        {
        case Type::parser:
        {
            return object.parser.getMomentum(x,y,z,engine);
        }
        case Type::gaussian:
        {
            return object.gaussian.getMomentum(x,y,z,engine);
        }
        case Type::gaussianflux:
        {
            return object.gaussianflux.getMomentum(x,y,z,engine);
        }
        case Type::uniform:
        {
            return object.uniform.getMomentum(x,y,z,engine);
        }
        case Type::maxwellian:
        {
            return object.maxwellian.getMomentum(x,y,z,engine);
        }
        case Type::juttner:
        {
            return object.juttner.getMomentum(x,y,z,engine);
        }
        case Type::constant:
        {
            return object.constant.getMomentum(x,y,z,engine);
        }
        default:
        {
            amrex::Abort("InjectorMomentum: unknown type");
            return {0.0,0.0,0.0};
        }
        }
    }
 
    // call getBulkMomentum from the object stored in the union
    // (the union is called Object, and the instance is called object).
    [[nodiscard]]
    AMREX_GPU_HOST_DEVICE
    amrex::XDim3
    getBulkMomentum (amrex::Real x, amrex::Real y, amrex::Real z) const noexcept
    {
        switch (type)
        {
        case Type::parser:
        {
            return object.parser.getBulkMomentum(x,y,z);
        }
        case Type::gaussian:
        {
            return object.gaussian.getBulkMomentum(x,y,z);
        }
        case Type::gaussianflux:
        {
            return object.gaussianflux.getBulkMomentum(x,y,z);
        }
        case Type::uniform:
        {
            return object.uniform.getBulkMomentum(x,y,z);
        }
        case Type::maxwellian:
        {
            return object.maxwellian.getBulkMomentum(x,y,z);
        }
        case Type::juttner:
        {
            return object.juttner.getBulkMomentum(x,y,z);
        }
        case Type::constant:
        {
            return object.constant.getBulkMomentum(x,y,z);
        }
        default:
        {
            amrex::Abort("InjectorMomentum: unknown type");
            return {0.0,0.0,0.0};
        }
        }
    }
 
    enum struct Type { constant, gaussian, gaussianflux, uniform, maxwellian, juttner, parser };
    Type type;
 
private:
 
    // An instance of union Object constructs and stores any one of
    // the objects declared (constant or gaussian or parser).
    union Object {
        Object (InjectorMomentumConstant*,
                amrex::Real a_ux, amrex::Real a_uy, amrex::Real a_uz) noexcept
            : constant(a_ux,a_uy,a_uz) {}
        Object (InjectorMomentumGaussian*,
                amrex::Real a_ux_m, amrex::Real a_uy_m,
                amrex::Real a_uz_m, amrex::Real a_ux_th,
                amrex::Real a_uy_th, amrex::Real a_uz_th) noexcept
            : gaussian(a_ux_m,a_uy_m,a_uz_m,a_ux_th,a_uy_th,a_uz_th) {}
        Object (InjectorMomentumGaussianFlux*,
                amrex::Real a_ux_m, amrex::Real a_uy_m,
                amrex::Real a_uz_m, amrex::Real a_ux_th,
                amrex::Real a_uy_th, amrex::Real a_uz_th,
                int a_flux_normal_axis, int a_flux_direction) noexcept
            : gaussianflux(a_ux_m,a_uy_m,a_uz_m,a_ux_th,a_uy_th,a_uz_th,a_flux_normal_axis,a_flux_direction) {}
        Object (InjectorMomentumUniform*,
                amrex::Real a_ux_min, amrex::Real a_uy_min,
                amrex::Real a_uz_min, amrex::Real a_ux_max,
                amrex::Real a_uy_max, amrex::Real a_uz_max) noexcept
            : uniform(a_ux_min,a_uy_min,a_uz_min,a_ux_max,a_uy_max,a_uz_max) {}
        Object (InjectorMomentumMaxwellian*,
                GetTemperatureVector const& t, GetVelocityVector const& b) noexcept
            : maxwellian(t,b) {}
        Object (InjectorMomentumJuttner*,
                GetTemperature const& t, GetVelocity const& b) noexcept
            : juttner(t,b) {}
        Object (InjectorMomentumParser*,
                GetVelocityVector const& a_velocity) noexcept
            : parser(a_velocity) {}
        InjectorMomentumConstant constant;
        InjectorMomentumGaussian gaussian;
        InjectorMomentumGaussianFlux gaussianflux;
        InjectorMomentumUniform uniform;
        InjectorMomentumMaxwellian maxwellian;
        InjectorMomentumJuttner juttner;
        InjectorMomentumParser parser;
    };
    Object object;
};
 
// In order for InjectorMomentum to be trivially copyable, its destructor
// must be trivial.  So we have to rely on a custom deleter for unique_ptr.
struct InjectorMomentumDeleter {
    void operator () (InjectorMomentum* p) const {
        if (p) {
            p->clear();
            delete p;
        }
    }
};
 
#endif //WARPX_INJECTOR_MOMENTUM_H_