maxwellian.hpp

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#ifndef MAXWELLIAN_HPP
#define MAXWELLIAN_HPP

class Maxwellian{
    double density;
    double temperature;
    double parallel_velocity;

    // Store inverse square root for efficient calculation
    double anisotropy_inv_sqrt; // Defined such that T = T_para*sqrt(1.0 + T_aniso*T_aniso);

    public:

    // Normal Maxwellian 
    Maxwellian(double density_in, double temperature_in)
      : density(density_in),
        temperature(temperature_in),
        parallel_velocity(0.0),
        anisotropy_inv_sqrt(1.0){}

    // Maxwellian with a parallel velocity and temperature anisotropy
    Maxwellian(double density_in, double temperature_in, double parallel_velocity_in, double anisotropy_in)
      : density(density_in),
        temperature(temperature_in),
        parallel_velocity(parallel_velocity_in),
        anisotropy_inv_sqrt(1.0/sqrt(anisotropy_in)){}

    // Get distribution function at (vpara, vperp) coordinate
    KOKKOS_INLINE_FUNCTION double get_f(double vpara, double vperp) const{
        double vpara_adj = (vpara - parallel_velocity)*anisotropy_inv_sqrt;
        double energy = 0.5*(vpara_adj*vpara_adj + vperp*vperp);
        double dist = vperp*density*anisotropy_inv_sqrt/temperature*exp(-energy);
        return dist;
    }
};

#endif