SUNDIALS Github Issue #66: https://github.com/LLNL/sundials/issues/66

compare_rhs.cpp

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#include <chrono>
#include <iostream>
#include <string>
#include <vector>

#include <nvector/nvector_serial.h>

struct lotka_volterra {
  static constexpr double rtol=1.e-12;
  static constexpr double atol=1.e-12;
  static constexpr int max_num_steps=1000000;

  const std::vector<double>& theta;
  long int n_eval;

  lotka_volterra(const std::vector<double>& theta0) :
    theta(theta0), n_eval(0)
  {}

  void print_n_eval(std::string info) {
    std::cout << "# of RHS evals ( " << info << " ) :" << n_eval << "\n";
  }

  void operator()(double t_in, N_Vector& y, N_Vector& ydot) {
    n_eval++;
    double alpha = theta[0];
    double beta = theta[1];
    double gamma = theta[2];
    double delta = theta[3];

    NV_Ith_S(ydot, 0) = (alpha - beta * NV_Ith_S(y, 1)) * NV_Ith_S(y, 0);
    NV_Ith_S(ydot, 1) = (-gamma + delta * NV_Ith_S(y, 0)) * NV_Ith_S(y, 1);
    /* double *ydata = NV_DATA_S(y); */
    /* double *yddata = NV_DATA_S(ydot); */    
    /* yddata[0] = (alpha - beta * ydata[1]) * ydata[0]; */
    /* yddata[1] = (-gamma + delta * ydata[0]) * ydata[1]; */
  }

  void operator()(const std::vector<double>& y, std::vector<double>& ydot, double t) {
    n_eval++;
    double alpha = theta[0];
    double beta = theta[1];
    double gamma = theta[2];
    double delta = theta[3];

    ydot[0] = (alpha - beta * y[1]) * y[0];
    ydot[1] = (-gamma + delta * y[0]) * y[1];
  }
};

void test_boost()
{
  int n = 2;
  std::vector<double> theta{1.5, 1.05, 1.5, 2.05};
  std::vector<double> y0{0.3, 0.8};
  lotka_volterra ode(theta);

  std::vector<double> ydot(n);

  const long int n_eval = 99999999;

  std::chrono::time_point<std::chrono::system_clock> start, end;
  std::chrono::duration<double, std::milli> elapsed;
  start = std::chrono::system_clock::now();
  for (long int i = 0; i < n_eval; ++i) {
    ode(y0, ydot, 0.1);
    y0[0] = ydot[0];
    y0[1] = ydot[1];
  }
  end = std::chrono::system_clock::now();
  elapsed = (end - start);

  std::cout << "odeint RHS elapsed time: " << elapsed.count() << " ms\n";
  std::cout << "odeint RHS count: " << ode.n_eval << "\n";
}

void test_arkode()
{
  int n = 2;
  std::vector<double> theta{1.5, 1.05, 1.5, 2.05};
  std::vector<double> y0{0.3, 0.8};
  std::vector<double> ydot(n);
  lotka_volterra ode(theta);

  N_Vector nvy0 = N_VMake_Serial(2, y0.data());
  N_Vector nvydot = N_VMake_Serial(2, ydot.data());

  const long int n_eval = 99999999;

  std::chrono::time_point<std::chrono::system_clock> start, end;
  std::chrono::duration<double, std::milli> elapsed;
  start = std::chrono::system_clock::now();
  for (long int i = 0; i < n_eval; ++i) {
    ode(0.1, nvy0, nvydot);
    y0[0] = ydot[0];
    y0[1] = ydot[1];
  }
  end = std::chrono::system_clock::now();
  elapsed = (end - start);

  std::cout << "arkode RHS elapsed time: " << elapsed.count() << " ms\n";
  std::cout << "arkode RHS count: " << ode.n_eval << "\n";
}

int main()
{
  test_boost();
  test_arkode();
  return 0;
}

compile

$ c++ --version
Apple clang version 12.0.0 (clang-1200.0.32.27)
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
$ c++ -std=c++11 -O3 -Isundials-master/instdir/include compare_rhs.cpp -o compare_rhs.03 -L sundials-master/instdir/lib/ -lsundials_arkode

Output:

$ ./compare_rhs.03
odeint RHS elapsed time: 367.858 ms
odeint RHS count: 99999999
arkode RHS elapsed time: 871.287 ms
arkode RHS count: 99999999

Built sundials 5.7.0 with the commands:

$ git clone https://github.com/LLNL/sundials.git sundials-master
$ cd sundials-master
$ mkdir build
$ cd build
$ cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER=$(which cc) -DCMAKE_INSTALL_PREFIX=../instdir -DEXAMPLES_INSTALL=OFF ../