public void OdeAiry()
{
// This is the airy differential equation
Func <double, double, double> f = (double x, double y) => x * y;
// Solutions should be of the form f(x) = a Ai(x) + b Bi(x).
// Given initial value of f and f', this equation plus the Wronskian can be solved to give
// a = \pi ( f Bi' - f' Bi ) b = \pi ( f' Ai - f Ai' )
// Start with some initial conditions
double x0 = 0.0;
double y0 = 0.0;
double yp0 = 1.0;
// Find the a and b coefficients consistent with those values
SolutionPair s0 = AdvancedMath.Airy(x0);
double a = Math.PI * (y0 * s0.SecondSolutionDerivative - yp0 * s0.SecondSolutionValue);
double b = Math.PI * (yp0 * s0.FirstSolutionValue - y0 * s0.FirstSolutionDerivative);
Assert.IsTrue(TestUtilities.IsNearlyEqual(y0, a * s0.FirstSolutionValue + b * s0.SecondSolutionValue));
Assert.IsTrue(TestUtilities.IsNearlyEqual(yp0, a * s0.FirstSolutionDerivative + b * s0.SecondSolutionDerivative));
// Integrate to a new point (pick a negative one so we test left integration)
double x1 = -5.0;
OdeResult result = FunctionMath.IntegrateConservativeOde(f, x0, y0, yp0, x1);
Assert.IsTrue(TestUtilities.IsNearlyEqual(result.X, x1));
Console.WriteLine(result.EvaluationCount);
// The solution should still hold
SolutionPair s1 = AdvancedMath.Airy(x1);
Assert.IsTrue(TestUtilities.IsNearlyEqual(result.Y, a * s1.FirstSolutionValue + b * s1.SecondSolutionValue, result.Settings));
Assert.IsTrue(TestUtilities.IsNearlyEqual(result.YPrime, a * s1.FirstSolutionDerivative + b * s1.SecondSolutionDerivative, result.Settings));
}
public void OdeSine()
{
// The sine and cosine functions satisfy
// y'' = - y
// This is perhaps the simplest conservative differential equation.
// (i.e. right hand side depends only on y, not y')
Func <double, double, double> f = (double x, double y) => - y;
int count = 0;
OdeSettings settings = new OdeSettings()
{
Listener = (OdeResult r) => {
Assert.IsTrue(TestUtilities.IsNearlyEqual(
MoreMath.Sqr(r.Y) + MoreMath.Sqr(r.YPrime), 1.0, r.Settings
));
Assert.IsTrue(TestUtilities.IsNearlyEqual(
r.Y, MoreMath.Sin(r.X), r.Settings
));
count++;
}
};
OdeResult result = FunctionMath.IntegrateConservativeOde(f, 0.0, 0.0, 1.0, 5.0, settings);
Assert.IsTrue(TestUtilities.IsNearlyEqual(result.Y, MoreMath.Sin(5.0)));
Assert.IsTrue(count > 0);
}
public static void IntegrateOde()
{
Func <double, double, double> rhs = (x, y) => - x * y;
OdeResult sln = FunctionMath.IntegrateOde(rhs, 0.0, 1.0, 2.0);
Console.WriteLine($"Numeric solution y({sln.X}) = {sln.Y}.");
Console.WriteLine($"Required {sln.EvaluationCount} evaluations.");
Console.WriteLine($"Analytic solution y({sln.X}) = {Math.Exp(-MoreMath.Sqr(sln.X) / 2.0)}");
// Lotka-Volterra equations
double A = 0.1;
double B = 0.02;
double C = 0.4;
double D = 0.02;
Func <double, IReadOnlyList <double>, IReadOnlyList <double> > lkRhs = (t, y) => {
return(new double[] {
A *y[0] - B * y[0] * y[1], D *y[0] * y[1] - C * y[1]
});
};
MultiOdeSettings lkSettings = new MultiOdeSettings()
{
Listener = r => { Console.WriteLine($"t={r.X} rabbits={r.Y[0]}, foxes={r.Y[1]}"); }
};
MultiFunctionMath.IntegrateOde(lkRhs, 0.0, new double[] { 20.0, 10.0 }, 50.0, lkSettings);
Func <double, IReadOnlyList <double>, IReadOnlyList <double> > rhs1 = (x, u) => {
return(new double[] { u[1], -u[0] });
};
MultiOdeSettings settings1 = new MultiOdeSettings()
{
EvaluationBudget = 100000
};
MultiOdeResult result1 = MultiFunctionMath.IntegrateOde(
rhs1, 0.0, new double[] { 0.0, 1.0 }, 500.0, settings1
);
double s1 = MoreMath.Sqr(result1.Y[0]) + MoreMath.Sqr(result1.Y[1]);
Console.WriteLine($"y({result1.X}) = {result1.Y[0]}, (y)^2 + (y')^2 = {s1}");
Console.WriteLine($"Required {result1.EvaluationCount} evaluations.");
Func <double, double, double> rhs2 = (x, y) => - y;
OdeSettings settings2 = new OdeSettings()
{
EvaluationBudget = 100000
};
OdeResult result2 = FunctionMath.IntegrateConservativeOde(
rhs2, 0.0, 0.0, 1.0, 500.0, settings2
);
double s2 = MoreMath.Sqr(result2.Y) + MoreMath.Sqr(result2.YPrime);
Console.WriteLine($"y({result2.X}) = {result2.Y}, (y)^2 + (y')^2 = {s2}");
Console.WriteLine($"Required {result2.EvaluationCount} evaluations");
Console.WriteLine(MoreMath.Sin(500.0));
}
private static double CoulombF_Integrate(int L, double eta, double rho)
{
// start at the series limit
double rho1 = Math.Min(
4.0 + 2.0 * Math.Sqrt(L),
(8.0 + 4.0 * L) / Math.Abs(eta)
);
double F, FP;
CoulombF_Series(L, eta, rho1, out F, out FP);
// TODO: switch so we integrate w/o the C factor, then apply it afterward
if ((F == 0.0) && (FP == 0.0))
{
return(0.0);
}
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => ((L * (L + 1) / x + 2.0 * eta) / x - 1.0) * y,
rho1, F, FP, rho,
new OdeEvaluationSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 8192 * 2
}
);
/*
* F = r.Y;
* FP = r.YPrime;
*
* // integrate out to rho
* BulrischStoerStoermerStepper s = new BulrischStoerStoermerStepper();
* s.RightHandSide = delegate(double x, double U) {
* return ((L * (L + 1) / x / x + 2.0 * eta / x - 1.0) * U);
* };
* s.X = rho0;
* s.Y = F;
* s.YPrime = FP;
* s.DeltaX = 0.25;
* s.Accuracy = 2.5E-13;
* s.Integrate(rho);
*/
// return the result
return(r.Y);
}
public void OdePendulum()
{
// Without the small-angle approximation, the period of a pendulum is not
// independent of angle. Instead, it is given by
// P = 4 K(\sin(\phi_0) / 2)
// where \phi_0 is the release angle and K is the complete elliptic function
// of the first kind.
// See https://en.wikipedia.org/wiki/Pendulum_(mathematics)
// We compute for an initial angle of 45 degrees, far beyond a small angle.
Func <double, double, double> rhs = (double t, double u) => - MoreMath.Sin(u);
double u0 = Math.PI / 4.0;
double p = 4.0 * AdvancedMath.EllipticK(MoreMath.Sin(u0 / 2.0));
OdeResult r = FunctionMath.IntegrateConservativeOde(rhs, 0.0, u0, 0.0, p);
Assert.IsTrue(TestUtilities.IsNearlyEqual(r.Y, u0));
Console.WriteLine(r.EvaluationCount);
}
public double Evaluate()
{
CoulombF_Series(L, eta, rho0, out double F, out double FP);
if ((F == 0.0) && (FP == 0.0))
{
return(0.0);
}
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => ((L * (L + 1) / x + 2.0 * eta) / x - 1.0) * y,
rho0, F, FP, rho,
new OdeSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 25000
}
);
double C = CoulombFactor(L, eta);
return(C * r.Y);
}
/// <summary>
/// Computes the irregular Coulomb wave function.
/// </summary>
/// <param name="L">The angular momentum number, which must be non-negative.</param>
/// <param name="eta">The charge parameter, which can be postive or negative.</param>
/// <param name="rho">The radial distance parameter, which must be non-negative.</param>
/// <returns>The value of G<sub>L</sub>(η,ρ).</returns>
/// <remarks>
/// <para>For information on the Coulomb wave functions, see the remarks on <see cref="Coulomb" />.</para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="L"/> or <paramref name="rho"/> is negative.</exception>
/// <seealso cref="Coulomb"/>
/// <seealso cref="CoulombF"/>
/// <seealso href="http://en.wikipedia.org/wiki/Coulomb_wave_function" />
/// <seealso href="http://mathworld.wolfram.com/CoulombWaveFunction.html" />
public static double CoulombG(int L, double eta, double rho)
{
if (L < 0)
{
throw new ArgumentOutOfRangeException(nameof(L));
}
if (rho < 0)
{
throw new ArgumentOutOfRangeException(nameof(rho));
}
if ((rho < 4.0) && Math.Abs(rho * eta) < 8.0)
{
// For small enough rho, use the power series for L=0, then recurse upward to desired L.
double F, FP, G, GP;
Coulomb_Zero_Series(eta, rho, out F, out FP, out G, out GP);
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
return(G);
}
else if (rho > 32.0 + (L * L + eta * eta) / 2.0)
{
// For large enough rho, use the asymptotic series.
SolutionPair s = Coulomb_Asymptotic(L, eta, rho);
return(s.SecondSolutionValue);
}
else
{
// Transition region
if (rho >= CoulombTurningPoint(L, eta))
{
// Beyond the turning point, use Steed's method.
SolutionPair result = Coulomb_Steed(L, eta, rho);
return(result.SecondSolutionValue);
}
else
{
// we will start at L=0 (which has a smaller turning point radius) and recurse up to the desired L
// this is okay because G increasees with increasing L
double G, GP;
double rho0 = 2.0 * eta;
if (rho < rho0)
{
// if inside the turning point even for L=0, start at the turning point and integrate in
// this is okay becaue G increases with decraseing rho
// use Steed's method at the turning point
// for large enough eta, we could use the turning point expansion at L=0, but it contributes
// a lot of code for little overall performance increase so we have chosen not to
SolutionPair result = Coulomb_Steed(0, eta, 2.0 * eta);
G = result.SecondSolutionValue;
GP = result.SecondSolutionDerivative;
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => (2.0 * eta / x - 1.0) * y,
rho0, G, GP, rho,
new OdeEvaluationSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 8192 * 2
}
);
G = r.Y;
GP = r.YPrime;
/*
* BulrischStoerStoermerStepper s = new BulrischStoerStoermerStepper();
* s.RightHandSide = delegate(double x, double U) {
* return ((2.0 * eta / x - 1.0) * U);
* };
* s.X = 2.0 * eta;
* s.Y = G;
* s.YPrime = GP;
* s.DeltaX = 0.25;
* s.Accuracy = 2.5E-13;
* s.Integrate(rho);
*
* G = s.Y;
* GP = s.YPrime;
*/
}
else
{
// if beyond the turning point for L=0, just use Steeds method
SolutionPair result = Coulomb_Steed(0, eta, rho);
G = result.SecondSolutionValue;
GP = result.SecondSolutionDerivative;
}
// Recurse up to the desired L.
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
return(G);
}
}
}
/// <summary>
/// Computes the regular and irregular Coulomb wave functions and their derivatives.
/// </summary>
/// <param name="L">The angular momentum number, which must be non-negative.</param>
/// <param name="eta">The charge parameter, which can be postive or negative.</param>
/// <param name="rho">The radial distance parameter, which must be non-negative.</param>
/// <returns>The values of F, F', G, and G' for the given parameters.</returns>
/// <remarks>
/// <para>The Coulomb wave functions are the radial wave functions of a non-relativistic particle in a Coulomb
/// potential.</para>
/// <para>They satisfy the differential equation:</para>
/// <img src="../images/CoulombODE.png" />
/// <para>A repulsive potential is represented by η > 0, an attractive potential by η < 0.</para>
/// <para>F is oscilatory in the region beyond the classical turning point. In the quantum tunneling region inside
/// the classical turning point, F is exponentially supressed and vanishes at the origin, while G grows exponentially and
/// diverges at the origin.</para>
/// <para>Many numerical libraries compute Coulomb wave functions in the quantum tunneling region using a WKB approximation,
/// which accurately determine only the first handfull of digits; our library computes Coulomb wave functions even in this
/// computationaly difficult region to nearly full precision -- all but the last 3-4 digits can be trusted.</para>
/// <para>The irregular Coulomb wave functions G<sub>L</sub>(η,ρ) are the complementary independent solutions
/// of the same differential equation.</para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="L"/> or <paramref name="rho"/> is negative.</exception>
/// <seealso cref="CoulombF"/>
/// <seealso cref="CoulombG"/>
/// <seealso href="http://en.wikipedia.org/wiki/Coulomb_wave_function" />
/// <seealso href="http://mathworld.wolfram.com/CoulombWaveFunction.html" />
public static SolutionPair Coulomb(int L, double eta, double rho)
{
if (L < 0)
{
throw new ArgumentOutOfRangeException(nameof(L));
}
if (rho < 0)
{
throw new ArgumentOutOfRangeException(nameof(rho));
}
if (rho == 0.0)
{
if (L == 0)
{
double C = CoulombFactor(L, eta);
return(new SolutionPair(0.0, C, 1.0 / C, Double.NegativeInfinity));
}
else
{
return(new SolutionPair(0.0, 0.0, Double.PositiveInfinity, Double.NegativeInfinity));
}
}
else if ((rho < 4.0) && Math.Abs(rho * eta) < 8.0)
{
// Below the safe series radius for L=0, compute using the series
double F, FP, G, GP;
Coulomb_Zero_Series(eta, rho, out F, out FP, out G, out GP);
// For higher L, recurse G upward, but compute F via the direct series.
// G is safe to compute via recursion and F is not because G is increasing
// rapidly and F is decreasing rapidly with increasing L.
if (L > 0)
{
CoulombF_Series(L, eta, rho, out F, out FP);
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
}
return(new SolutionPair(F, FP, G, GP));
}
else if (rho > 32.0 + (L * L + eta * eta) / 2.0)
{
return(Coulomb_Asymptotic(L, eta, rho));
}
else
{
double rho0 = CoulombTurningPoint(L, eta);
if (rho > rho0)
{
return(Coulomb_Steed(L, eta, rho));
}
else
{
// First F
double F, FP;
double rho1 = Math.Min(
4.0 + 2.0 * Math.Sqrt(L),
(8.0 + 4.0 * L) / Math.Abs(eta)
);
if (rho < rho1)
{
CoulombF_Series(L, eta, rho, out F, out FP);
}
else
{
CoulombF_Series(L, eta, rho1, out F, out FP);
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => ((L * (L + 1) / x + 2.0 * eta) / x - 1.0) * y,
rho1, F, FP, rho,
new OdeEvaluationSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 8192 * 2
}
);
F = r.Y;
FP = r.YPrime;
}
// Then G
double G, GP;
// For L = 0 the transition region is smaller, so we will determine G
// at L = 0, where non-integration methods apply over a larger region,
// and then recurse upward.
double rho2 = CoulombTurningPoint(0, eta);
if (rho > 32.0 + eta * eta / 2.0)
{
SolutionPair s = Coulomb_Asymptotic(0, eta, rho);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
}
else if (rho > rho2)
{
SolutionPair s = Coulomb_Steed(0, eta, rho);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
}
else
{
SolutionPair s = Coulomb_Steed(0, eta, rho2);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
// Integrate inward from turning point.
// G increases and F decreases in this direction, so this is stable.
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => (2.0 * eta / x - 1.0) * y,
rho2, G, GP, rho,
new OdeEvaluationSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 8192 * 2
}
);
G = r.Y;
GP = r.YPrime;
}
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
return(new SolutionPair(F, FP, G, GP));
}
}
}
/// <summary>
/// Computes the irregular Coulomb wave function.
/// </summary>
/// <param name="L">The angular momentum number, which must be non-negative.</param>
/// <param name="eta">The charge parameter, which can be positive or negative.</param>
/// <param name="rho">The radial distance parameter, which must be non-negative.</param>
/// <returns>The value of G<sub>L</sub>(η,ρ).</returns>
/// <remarks>
/// <para>For information on the Coulomb wave functions, see the remarks on <see cref="Coulomb" />.</para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="L"/> or <paramref name="rho"/> is negative.</exception>
/// <seealso cref="Coulomb"/>
/// <seealso cref="CoulombF"/>
/// <seealso href="http://en.wikipedia.org/wiki/Coulomb_wave_function" />
/// <seealso href="http://mathworld.wolfram.com/CoulombWaveFunction.html" />
public static double CoulombG(int L, double eta, double rho)
{
if (L < 0)
{
throw new ArgumentOutOfRangeException(nameof(L));
}
if (rho < 0)
{
throw new ArgumentOutOfRangeException(nameof(rho));
}
if (rho <= Coulomb_Series_Limit(0, eta))
{
// For small enough rho, use the power series for L=0, then recurse upward to desired L.
Coulomb_Zero_Series(eta, rho, out double F, out double FP, out double G, out double GP);
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
return(G);
}
else if (rho >= Coulomb_Asymptotic_Limit(L, eta))
{
// For large enough rho, use the asymptotic series.
SolutionPair s = Coulomb_Asymptotic(L, eta, rho);
return(s.SecondSolutionValue);
}
else if (rho >= CoulombTurningPoint(L, eta))
{
// Beyond the turning point, use Steed's method.
SolutionPair result = Coulomb_Steed(L, eta, rho);
return(result.SecondSolutionValue);
}
else
{
// We will start at L=0 (which has a smaller turning point radius) and recurse up to the desired L.
// This is okay because G increases with increasing L. We already know that we are beyond the L=0
// series limit; otherwise we would have taken the branch for it above. We might still be
// in the asymptotic region, in the Steed region, below the L=0 turning point (if \eta > 0).
double G, GP;
if (rho >= Coulomb_Asymptotic_Limit(0, eta))
{
SolutionPair s = Coulomb_Asymptotic(0, eta, rho);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
}
else
{
double rho1 = CoulombTurningPoint(0, eta);
if (rho >= rho1)
{
SolutionPair s = Coulomb_Steed(0, eta, rho);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
}
else
{
SolutionPair s = Coulomb_Steed(0, eta, rho1);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => (2.0 * eta / x - 1.0) * y,
rho1, G, GP, rho,
new OdeSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 25000
}
);
G = r.Y;
GP = r.YPrime;
}
}
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
return(G);
}
}
/// <summary>
/// Computes the regular and irregular Coulomb wave functions and their derivatives.
/// </summary>
/// <param name="L">The angular momentum number, which must be non-negative.</param>
/// <param name="eta">The charge parameter, which can be positive or negative.</param>
/// <param name="rho">The radial distance parameter, which must be non-negative.</param>
/// <returns>The values of F, F', G, and G' for the given parameters.</returns>
/// <remarks>
/// <para>The Coulomb wave functions are the radial wave functions of a non-relativistic particle in a Coulomb
/// potential.</para>
/// <para>They satisfy the differential equation:</para>
/// <img src="../images/CoulombODE.png" />
/// <para>A repulsive potential is represented by η > 0, an attractive potential by η < 0.</para>
/// <para>F is oscillatory in the region beyond the classical turning point. In the quantum tunneling region inside
/// the classical turning point, F is exponentially suppressed and vanishes at the origin, while G grows exponentially and
/// diverges at the origin.</para>
/// <para>Many numerical libraries compute Coulomb wave functions in the quantum tunneling region using a WKB approximation,
/// which accurately determine only the first few decimal digits; our library computes Coulomb wave functions even in this
/// computationally difficult region to nearly full precision -- all but the last 4-5 decimal digits can be trusted.</para>
/// <para>The irregular Coulomb wave functions G<sub>L</sub>(η,ρ) are the complementary independent solutions
/// of the same differential equation.</para>
/// </remarks>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="L"/> or <paramref name="rho"/> is negative.</exception>
/// <seealso cref="CoulombF"/>
/// <seealso cref="CoulombG"/>
/// <seealso href="http://en.wikipedia.org/wiki/Coulomb_wave_function" />
/// <seealso href="http://mathworld.wolfram.com/CoulombWaveFunction.html" />
public static SolutionPair Coulomb(int L, double eta, double rho)
{
if (L < 0)
{
throw new ArgumentOutOfRangeException(nameof(L));
}
if (rho < 0)
{
throw new ArgumentOutOfRangeException(nameof(rho));
}
if (rho == 0.0)
{
if (L == 0)
{
double C = CoulombFactor(L, eta);
return(new SolutionPair(0.0, C, 1.0 / C, Double.NegativeInfinity));
}
else
{
return(new SolutionPair(0.0, 0.0, Double.PositiveInfinity, Double.NegativeInfinity));
}
}
else if (rho <= Coulomb_Series_Limit(0, eta))
{
// Below the safe series radius for L=0, compute using the series.
Coulomb_Zero_Series(eta, rho, out double F, out double FP, out double G, out double GP);
// For higher L, recurse G upward, but compute F via the direct series.
// G is safe to compute via recursion and F is not because G is increasing
// rapidly and F is decreasing rapidly with increasing L. Since the series
// for F was good for L = 0, it's certainly good for L > 0.
if (L > 0)
{
CoulombF_Series(L, eta, rho, out F, out FP);
double C = CoulombFactor(L, eta);
F *= C;
FP *= C;
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
}
return(new SolutionPair(F, FP, G, GP));
}
else if (rho >= Coulomb_Asymptotic_Limit(L, eta))
{
return(Coulomb_Asymptotic(L, eta, rho));
}
else if (rho >= CoulombTurningPoint(L, eta))
{
return(Coulomb_Steed(L, eta, rho));
}
else
{
// This code is copied from CoulombG; factor it into a seperate method.
double G, GP;
if (rho >= Coulomb_Asymptotic_Limit(0, eta))
{
SolutionPair s = Coulomb_Asymptotic(0, eta, rho);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
}
else
{
double rho1 = CoulombTurningPoint(0, eta);
if (rho >= rho1)
{
SolutionPair s = Coulomb_Steed(0, eta, rho);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
}
else
{
SolutionPair s = Coulomb_Steed(0, eta, rho1);
G = s.SecondSolutionValue;
GP = s.SecondSolutionDerivative;
OdeResult r = FunctionMath.IntegrateConservativeOde(
(double x, double y) => (2.0 * eta / x - 1.0) * y,
rho1, G, GP, rho,
new OdeSettings()
{
RelativePrecision = 2.5E-13,
AbsolutePrecision = 0.0,
EvaluationBudget = 25000
}
);
G = r.Y;
GP = r.YPrime;
}
}
Coulomb_Recurse_Upward(0, L, eta, rho, ref G, ref GP);
// We can determine F and FP via CF1 and Wronskian, but if we are within
// series limit, it's likely a little faster and more accurate.
double F, FP;
if (rho < Coulomb_Series_Limit(L, eta))
{
CoulombF_Series(L, eta, rho, out F, out FP);
double C = CoulombFactor(L, eta);
F *= C;
FP *= C;
}
else
{
double f = Coulomb_CF1(L, eta, rho, out int _);
F = 1.0 / (f * G - GP);
FP = f * F;
}
return(new SolutionPair(F, FP, G, GP));
}
}
