Removing particles from simulations (C)

This example demonstrates different options for removing particles from the simulation.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include "rebound.h"

void print_hashes(struct reb_simulation* r){
    printf("hashes = ");
    for (int i=0;i<r->N;i++){
        printf("%u ", r->particles[i].hash);
    }
    printf("\n");
}


int main(int argc, char* argv[]){
    // Note that when using a tree (for gravity calculation or collision search), you need
    // to call reb_tree_update(r) after removing particles. Only then is the particle
    // removed. This helps avoiding to rebuild the tree multiple times if more than one
    // particle is removed at the same time.
    struct reb_simulation* r = reb_create_simulation();

    for (int i=0;i<9;i++){
        struct reb_particle p = {0};
        p.hash = i;
        reb_add(r, p);
    }

    struct reb_particle p = {0};
    p.hash = reb_hash("Planet 9");
    reb_add(r, p);

    printf("Initial hashes:\n");
    print_hashes(r);

    int success;
    int keepSorted = 0;
    printf("\nTry to remove index 3 (4th particle)...\n");
    success = reb_remove(r, 3, keepSorted);
    if (success){
        printf("Particle successfully removed\n");
    }
    print_hashes(r);
    printf("Because keepSorted = 0, last particle replaced removed particle and indices got scrambled:\n\n");

    keepSorted = 1;
    printf("Try to remove index 6 (7th particle)  while preserving the order with keepSorted=1...\n");
    success = reb_remove(r, 6, keepSorted);
    if (success){
        printf("Particle successfully removed\n");
    }
    print_hashes(r);

    printf("\nWe can also remove particles by the hashes we assign them (this is robust to particles switching indices in the particles array during the simulation).\n");
    printf("Try to remove Planet 9...\n");
    success = reb_remove_by_hash(r, reb_hash("Planet 9"), keepSorted);
    if (success){
        printf("Particle successfully removed\n");
    }
    print_hashes(r);

    printf("\nFinally, we can remove particles by their hash directly.\n");
    success = reb_remove_by_hash(r, 1, keepSorted);
    if (success){
        printf("Particle successfully removed\n");
    }
    print_hashes(r);

    printf("\nAlso, if we try to remove an index > N, we get an error and no particle is removed:\n");
    printf("Try to remove index 15...\n");
    success = reb_remove(r, 15, keepSorted);
    if (success){
        printf("Particle successfully removed\n");
    }
}

This example is located in the directory examples/removing_particles_from_simulation