# Simulation Archive (C)¶

This example shows how to use the Simulation Archive. We integrate a two planet system forward in time using the WHFast integrator. The simulation can be interrupted at any time. On the next run, the program will try to reload the latest data from the Simulation Archive.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <math.h>
#include <sys/time.h>
#include <sys/stat.h>
#include "rebound.h"

int main(int argc, char* argv[]) {
char* filename = "simulationarchive.bin";

// Trying to open a SimulationArchive file
struct reb_simulationarchive* sa = reb_open_simulationarchive(filename);
if (sa==NULL){
printf("Can not open file.\n");
}
// Get a simulation from the file (if possible, otherwise NULL is returned)
struct reb_simulation* r = reb_create_simulation_from_simulationarchive(sa,-1);
// Whenever you've opened a SimulationArchive and don't need it anymore, close it.
reb_close_simulationarchive(sa);
// Check if we were successful
if (r==NULL){
printf("No simulation archive found. Creating new simulation.\n");
r= reb_create_simulation();
struct reb_particle star = {.m=1.};
struct reb_particle planet1 = reb_tools_orbit2d_to_particle(r->G, star, 1e-3, 1., 0.01, 0., 0.);
struct reb_particle planet2 = reb_tools_orbit2d_to_particle(r->G, star, 1e-3, 2.3, 0.01, 0., 0.);
reb_move_to_com(r);
r->dt = 6./365.25*2.*M_PI;              // 6 days in units where G=1
r->ri_whfast.safe_mode = 0;             // The SimulationArchive works with both safe_mode on and off
r->ri_whfast.corrector = 5;
r->integrator = REB_INTEGRATOR_WHFAST;
}else{
printf("Found simulation archive. Loaded snapshot at t=%.16f.\n",r->t);
}

// Automatically create a snapshot every 100 time units
reb_simulationarchive_automate_interval(r,filename,100.);
// Alternatively, you can also create a snapshot every 5 seconds (walltime)
//reb_simulationarchive_automate_walltime(r,filename,5.);

// Run the integration (this will be very quick in this example)
reb_integrate(r, r->t+2000); // integrate (a little further than where we currently are)
printf("Final time: %f\n",r->t);

// You can also manually append a snapshot
reb_simulationarchive_snapshot(r,filename);

// Free the simulation to free up memory
reb_free_simulation(r);
}


This example is located in the directory examples/simulationarchive