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Fix the "apocalypse" bug that was causing celestials to be suddenly moved to random locations #612

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merged 7 commits into from
Aug 9, 2015
Merged

Fix the "apocalypse" bug that was causing celestials to be suddenly moved to random locations #612

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87815c4
More traces, better check.
pleroy Aug 9, 2015
705fe27
Moar traces.
pleroy Aug 9, 2015
0dfbb23
Fix the bug.
pleroy Aug 9, 2015
1bba03e
Remove the right log.
pleroy Aug 9, 2015
fe8259b
stl logging.
pleroy Aug 9, 2015
7692511
Lint.
pleroy Aug 9, 2015
557fc3a
After egg's review.
pleroy Aug 9, 2015
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16 changes: 13 additions & 3 deletions physics/continuous_trajectory_body.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
#include <limits>
#include <vector>

#include "glog/stl_logging.h"
#include "physics/continuous_trajectory.hpp"
#include "quantities/si.hpp"
#include "testing_utilities/numerics.hpp"
Expand Down Expand Up @@ -269,11 +270,13 @@ void ContinuousTrajectory<Frame>::ComputeBestNewhallApproximation(
std::vector<Velocity<Frame>> const& v,
Instant const& t_min,
Instant const& t_max)) {
Length const previous_adjusted_tolerance = adjusted_tolerance_;

// If the degree is too old, restart from the lowest degree. This ensures
// that we use the lowest possible degree at a small computational cost.
if (degree_age_ >= kMaxDegreeAge) {
VLOG(1) << "Lowering degree from " << degree_ << " to " << kMinDegree
<< " because the approximation is too old";
VLOG(1) << "Lowering degree for " << this << " from " << degree_
<< " to " << kMinDegree << " because the approximation is too old";
is_unstable_ = false;
adjusted_tolerance_ = tolerance_;
degree_ = kMinDegree;
Expand All @@ -292,7 +295,8 @@ void ContinuousTrajectory<Frame>::ComputeBestNewhallApproximation(
// If we are in the zone of numerical instabilities and we exceeded the
// tolerance, restart from the lowest degree.
if (is_unstable_ && error_estimate > adjusted_tolerance_) {
VLOG(1) << "Lowering degree from " << degree_ << " to " << kMinDegree
VLOG(1) << "Lowering degree for " << this << " from " << degree_
<< " to " << kMinDegree
<< " because error estimate " << error_estimate
<< " exceeds adjusted tolerance " << adjusted_tolerance_
<< " and computations are unstable";
Expand Down Expand Up @@ -338,6 +342,12 @@ void ContinuousTrajectory<Frame>::ComputeBestNewhallApproximation(
<< " with error estimate " << error_estimate;
}

// A check that the tolerance did not explode.
CHECK_LT(adjusted_tolerance_, 1E6 * previous_adjusted_tolerance)
<< "Apocalypse occurred at " << time
<< ", displacements are: " << q
<< ", velocities are: " << v;

++degree_age_;
}

Expand Down
10 changes: 6 additions & 4 deletions physics/ephemeris_body.hpp
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Expand Up @@ -121,6 +121,9 @@ Ephemeris<Frame>::Ephemeris(
inserted.first->second.get();
trajectory->Append(initial_time, degrees_of_freedom);

VLOG(1) << "Constructed trajectory " << trajectory
<< " for body with mass " << body->mass();

if (body->is_oblate()) {
// Inserting at the beginning of the vectors is O(N).
oblate_bodies_.insert(oblate_bodies_.begin(), body.get());
Expand Down Expand Up @@ -210,9 +213,8 @@ void Ephemeris<Frame>::ForgetAfter(Instant const & t) {
CHECK_LE(t, it->time.value);

int index = 0;
for (auto& pair : bodies_to_trajectories_) {
ContinuousTrajectory<Frame>& trajectory = *pair.second;
trajectory.ForgetAfter(
for (auto const& trajectory : trajectories_) {
trajectory->ForgetAfter(
it->time.value,
DegreesOfFreedom<Frame>(it->positions[index].value,
it->velocities[index].value));
Expand Down Expand Up @@ -309,7 +311,7 @@ void Ephemeris<Frame>::FlowWithFixedStep(
std::vector<not_null<Trajectory<Frame>*>> const& trajectories,
Time const& step,
Instant const& t) {
LOG(INFO) << __FUNCTION__;
VLOG(1) << __FUNCTION__ << " " << NAMED(step) << " " << NAMED(t);
if (empty() || t > t_max()) {
Prolong(t);
}
Expand Down
4 changes: 3 additions & 1 deletion physics/ephemeris_test.cpp
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Expand Up @@ -56,8 +56,10 @@ class EphemerisTest : public testing::Test {
initial_state,
not_null<Position<EarthMoonOrbitPlane>*> const centre_of_mass,
not_null<Time*> const period) {
auto earth = std::make_unique<MassiveBody const>(6E24 * Kilogram);
// Create the Moon before the Earth to exercise a bug caused by the order of
// pointers differing from the order of bodies (don't ask).
auto moon = std::make_unique<MassiveBody const>(7E22 * Kilogram);
auto earth = std::make_unique<MassiveBody const>(6E24 * Kilogram);

// The Earth-Moon system, roughly, with a circular orbit with velocities
// in the centre-of-mass frame.
Expand Down