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DP5Tests.cs
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DP5Tests.cs
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/*
* Copyright Lamont Granquist, Sebastien Gaggini and the MechJeb contributors
* SPDX-License-Identifier: MIT-0 OR LGPL-2.1+ OR CC0-1.0
*/
using System;
using System.Collections.Generic;
using AssertExtensions;
using MechJebLib.Core;
using MechJebLib.Core.ODE;
using MechJebLib.Primitives;
using Xunit;
using static MechJebLib.Utils.Statics;
using static System.Math;
namespace MechJebLibTest.MathsTests
{
public class DP5Tests
{
private class SimpleOscillator
{
private readonly double _k;
private readonly double _m;
public SimpleOscillator(double k, double m)
{
_k = k;
_m = m;
}
public int N => 2;
public void dydt(IList<double> y, double x, IList<double> dy)
{
dy[0] = y[1];
dy[1] = -_k / _m * y[0];
}
}
[Fact]
public void SimpleOscillatorTest()
{
var random = new Random();
const int NTRIALS = 50;
for (int n = 0; n < NTRIALS; n++)
{
double k = 2 * random.NextDouble() + 1;
double m = 2 * random.NextDouble() + 1;
double x0 = 4 * random.NextDouble() - 2;
double v0 = 4 * random.NextDouble() - 2;
double t0 = 4 * random.NextDouble() - 2;
double tf = 4 * random.NextDouble() - 2;
int count1 = random.Next(20, 40);
int count2 = random.Next(5, 40);
var solver = new DP5 { Interpnum = count1, Rtol = 1e-9, Atol = 0, Maxiter = 2000 };
var ode = new SimpleOscillator(k, m);
var f = new Action<IList<double>, double, IList<double>>(ode.dydt);
using var y0 = Vn.Rent(2);
y0[0] = x0;
y0[1] = v0;
using var yf = Vn.Rent(2);
double omega = Sqrt(k / m);
double dt = (tf - t0) / count1;
double dt2 = (tf - t0) / count2;
double[] expected = new double[count1 + 1];
for (int i = 0; i <= count1; i++)
{
double t = t0 + dt * i;
expected[i] = x0 * Cos(omega * (t - t0)) + v0 * Sin(omega * (t - t0)) / omega;
}
double[] expected2 = new double[count2 + 1];
for (int i = 0; i <= count2; i++)
{
double t = t0 + dt2 * i;
expected2[i] = x0 * Cos(omega * (t - t0)) + v0 * Sin(omega * (t - t0)) / omega;
}
for (int i = 0; i <= count1; i++)
{
double t = t0 + dt * i;
solver.Solve(f, y0, yf, t0, t);
yf[0].ShouldEqual(expected[i], 4e-6);
}
using (var interpolant = Hn.Get(ode.N))
{
solver.Solve(f, y0, yf, t0, tf, interpolant);
for (int i = 0; i <= count1; i++)
{
double t = t0 + dt * i;
using Vn y = interpolant.Evaluate(t);
y[0].ShouldEqual(expected[i], 4e-6);
}
for (int i = 0; i <= count2; i++)
{
double t = t0 + dt2 * i;
using Vn y = interpolant.Evaluate(t);
y[0].ShouldEqual(expected2[i], 2e-2);
}
}
long start = GC.GetAllocatedBytesForCurrentThread();
using (var interpolant = Hn.Get(ode.N))
{
solver.Solve(f, y0, yf, t0, tf, interpolant);
for (int i = 0; i <= count1; i++)
{
double t = t0 + dt * i;
using Vn y = interpolant.Evaluate(t);
y[0].ShouldEqual(expected[i], 4e-6);
}
for (int i = 0; i <= count2; i++)
{
double t = t0 + dt2 * i;
using Vn y = interpolant.Evaluate(t);
y[0].ShouldEqual(expected2[i], 2e-2);
}
}
Assert.Equal(0, GC.GetAllocatedBytesForCurrentThread() - start);
}
}
private class VacuumKernel
{
public int N => 6;
public void dydt(IList<double> yin, double x, IList<double> dyout)
{
var r = new V3(yin[0], yin[1], yin[2]);
var v = new V3(yin[3], yin[4], yin[5]);
double rm2 = r.sqrMagnitude;
double rm = Sqrt(rm2);
double rm3 = rm2 * rm;
V3 dr = v;
V3 dv = -r / rm3;
dyout.Set(0, dr);
dyout.Set(3, dv);
}
}
private static double Func(double t, IList<double> y, AbstractIVP i)
{
var r = new V3(y[0], y[1], y[2]);
return r.magnitude - 1.5;
}
[Fact]
public void AltitudeEventTest()
{
var ode = new VacuumKernel();
var solver = new DP5 { Rtol = 1e-9, Atol = 1e-9, Maxiter = 2000 };
var r0 = new V3(1, 0, 0);
var v0 = new V3(0, 1.3, 0);
var e = new List<Event> { new Event(Func) };
double[] y0 = new double[6];
double[] yf = new double[6];
y0.Set(0, r0);
y0.Set(3, v0);
solver.Solve(ode.dydt, y0, yf, 0, 10, events: e);
e[0].Time.ShouldEqual(Maths.TimeToNextRadius(1.0, r0, v0, 1.5), 1e-9);
}
}
}