131 lines
No EOL
3.9 KiB
C++
131 lines
No EOL
3.9 KiB
C++
#include <algorithm>
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#include <fstream>
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#include <gsl/gsl_errno.h>
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#include <gsl/gsl_math.h>
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#include <gsl/gsl_odeiv2.h>
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#include <gsl/gsl_spline.h>
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#include <iostream>
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#include <numeric>
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#include <string>
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#include <stdexcept>
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#include <vector>
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#include "loadtxt.h"
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extern "C" const int gsl_success() { return GSL_SUCCESS; } // It's zero, but just for clarity sake.
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// Our units are {kiloparsec, solar mass, gigayear}
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constexpr double G = 4.498317481097514e-06;
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class Interp {
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public:
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Interp(std::vector<double>& x, std::vector<double>& y)
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{
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acc = gsl_interp_accel_alloc();
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spline = gsl_spline_alloc(gsl_interp_cspline, x.size());
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gsl_spline_init(spline, x.data(), y.data(), x.size());
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}
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Interp() {}
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inline double operator()(double x) const
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{
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return gsl_spline_eval(spline, x, acc);
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}
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private:
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gsl_interp_accel *acc;
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gsl_spline *spline;
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};
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class Plummer {
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public:
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Plummer(double M, double b)
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: M(M), b(b) {}
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void calc_acceleration(const double *pos, double *acc)
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{
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double r2 = (pos[0]*pos[0] + pos[1]*pos[1] + pos[2]*pos[2] + b*b);
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double r = sqrt(r2);
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double r3_inv = 1/(r*r2);
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acc[0] = -G*M*pos[0]*r3_inv;
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acc[1] = -G*M*pos[1]*r3_inv;
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acc[2] = -G*M*pos[2]*r3_inv;
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}
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private:
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double M, b;
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};
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class Galaxy {
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public:
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Galaxy(std::string file_name)
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{
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auto data = Loadtxt("file.dat", {1, 2, 3}).get_cols();
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auto& t_data = data[0];
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auto& halo_m_data = data[1];
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auto& halo_b_data = data[2];
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std::transform(t_data.begin(), t_data.end(), t_data.begin(), [](const double& x){ return x-2.145; });
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std::transform(halo_b_data.begin(), halo_b_data.end(), halo_b_data.begin(), [](const double& x){ return x*0.7664209365408798; });
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interp_halo_m = Interp(t_data, halo_m_data);
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interp_halo_b = Interp(t_data, halo_b_data);
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}
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int func(double t, const double y[], double f[], void *params)
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{
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double halo_m = interp_halo_m(t);
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double halo_b = interp_halo_b(t);
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Plummer plummer(halo_m, halo_b);
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f[0] = y[3]; // vx -> x'
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f[1] = y[4]; // vy -> y'
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f[2] = y[5]; // vz -> z'
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plummer.calc_acceleration(y, f+3); // a -> v'
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return GSL_SUCCESS;
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}
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private:
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Interp interp_halo_m;
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Interp interp_halo_b;
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} galaxy("file.dat");
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// Not very nice to have it as a global variable but GSL will have problem otherwise.
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int jac(double t, const double y[], double *dfdy, double dfdt[], void *params) { return GSL_SUCCESS; }
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inline int func(double t, const double y[], double f[], void *params)
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{
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return galaxy.func(t, y, f, params);
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}
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extern "C"
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int integrate(const double y0[], const double t_max, const double step_size, double y[])
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{
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double t = 0;
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constexpr double h = 1./4096.;
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if (step_size/h - (int)(step_size/h) != 0) throw std::runtime_error("step_size must be a multiple of h");
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constexpr double epsabs = 1e-7;
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constexpr double epsrel = 0;
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const gsl_odeiv2_step_type *T = gsl_odeiv2_step_rk8pd;
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gsl_odeiv2_step *s = gsl_odeiv2_step_alloc(T, 6);
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gsl_odeiv2_evolve *e = gsl_odeiv2_evolve_alloc(6);
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gsl_odeiv2_control *c = gsl_odeiv2_control_y_new(epsabs, 0);
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gsl_odeiv2_system sys = {func, jac, 6, nullptr};
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gsl_odeiv2_driver *d = gsl_odeiv2_driver_alloc_y_new(&sys, T, h, epsabs, epsrel);
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int step = 0;
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const int step_max = t_max / step_size;
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std::copy(y0, y0+6, y);
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for (int step=0; step<step_max; step++) {
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std::copy(y+step*6, y+(step+1)*6, y+(step+1)*6);
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int status = gsl_odeiv2_driver_apply(d, &t, (step+1)*step_size, y+(step+1)*6);
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if (status != GSL_SUCCESS) return status;
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}
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return GSL_SUCCESS;
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}
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int main()
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{
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std::cout << "bye" << std::endl;
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double y[12];
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double y0[] = {80,0,0,0,80,0};
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for (int i=0; i<30000; i++)
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integrate(y0, 10, 10, y);
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return 0;
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} |