vibe coding an orbital mechanics simulation to try out claude code
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#include <catch2/catch_test_macros.hpp>
#include <catch2/matchers/catch_matchers_floating_point.hpp>
#include "../src/physics.h"
#include "../src/simulation.h"
#include "../src/config_loader.h"
#include "../src/test_utilities.h"
#include <cmath>
using Catch::Matchers::WithinAbs;
SCENARIO("Energy conservation in circular orbit", "[energy][sanity]") {
const double TIME_STEP = 60.0;
const double DAYS_TO_SIMULATE = 10.0;
const double SECONDS_PER_DAY = 86400.0;
SimulationState* sim = create_simulation(2, 0, 0, TIME_STEP);
REQUIRE(load_system_config(sim, "tests/test_energy.toml"));
const double initial_energy = calculate_system_total_energy(sim);
double total_time = DAYS_TO_SIMULATE * SECONDS_PER_DAY;
while (sim->time < total_time) {
update_simulation(sim);
}
const double final_energy = calculate_system_total_energy(sim);
const double energy_drift = fabs(final_energy - initial_energy) / fabs(initial_energy);
INFO("Initial energy: " << initial_energy << " J");
INFO("Final energy: " << final_energy << " J");
INFO("Relative drift: " << energy_drift << " (fraction)");
REQUIRE_THAT(energy_drift, WithinAbs(0.0, 1e-12));
destroy_simulation(sim);
}
SCENARIO("Orbit direction for zero inclination", "[direction][sanity]") {
const double TIME_STEP = 60.0;
const int STEPS = 1440; // 1 day at 60s steps
SimulationState* sim = create_simulation(2, 0, 0, TIME_STEP);
REQUIRE(load_system_config(sim, "tests/test_energy.toml"));
CelestialBody* sun = &sim->bodies[0];
CelestialBody* earth = &sim->bodies[1];
Vec3 initial_rel = vec3_sub(earth->global_position, sun->global_position);
const double theta_start = atan2(initial_rel.y, initial_rel.x);
for (int i = 0; i < STEPS; i++) update_simulation(sim);
Vec3 final_rel = vec3_sub(earth->global_position, sun->global_position);
const double delta = atan2(final_rel.y, final_rel.x) - theta_start;
INFO("Delta: " << delta << " rad");
REQUIRE_THAT(delta, WithinAbs(0.0172042841, 1e-6));
destroy_simulation(sim);
}