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58 lines
2.1 KiB
58 lines
2.1 KiB
// David Eberly, Geometric Tools, Redmond WA 98052
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// Copyright (c) 1998-2021
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// Distributed under the Boost Software License, Version 1.0.
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// https://www.boost.org/LICENSE_1_0.txt
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// https://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
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// Version: 4.0.2019.08.13
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#pragma once
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#include <Mathematics/OdeSolver.h>
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// The TVector template parameter allows you to create solvers with
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// Vector<N,Real> when the dimension N is known at compile time or
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// GVector<Real> when the dimension N is known at run time. Both classes
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// have 'int GetSize() const' that allow OdeSolver-derived classes to query
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// for the dimension.
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namespace gte
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{
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template <typename Real, typename TVector>
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class OdeRungeKutta4 : public OdeSolver<Real, TVector>
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{
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public:
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// Construction and destruction.
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virtual ~OdeRungeKutta4() = default;
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OdeRungeKutta4(Real tDelta, std::function<TVector(Real, TVector const&)> const& F)
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:
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OdeSolver<Real, TVector>(tDelta, F)
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{
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}
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// Estimate x(t + tDelta) from x(t) using dx/dt = F(t,x). You may
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// allow xIn and xOut to be the same object.
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virtual void Update(Real tIn, TVector const& xIn, Real& tOut, TVector& xOut) override
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{
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// Compute the first step.
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Real halfTDelta = (Real)0.5 * this->mTDelta;
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TVector fTemp1 = this->mFunction(tIn, xIn);
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TVector xTemp = xIn + halfTDelta * fTemp1;
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// Compute the second step.
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Real halfT = tIn + halfTDelta;
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TVector fTemp2 = this->mFunction(halfT, xTemp);
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xTemp = xIn + halfTDelta * fTemp2;
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// Compute the third step.
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TVector fTemp3 = this->mFunction(halfT, xTemp);
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xTemp = xIn + this->mTDelta * fTemp3;
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// Compute the fourth step.
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Real sixthTDelta = this->mTDelta / (Real)6;
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tOut = tIn + this->mTDelta;
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TVector fTemp4 = this->mFunction(tOut, xTemp);
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xOut = xIn + sixthTDelta * (fTemp1 + (Real)2 * (fTemp2 + fTemp3) + fTemp4);
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}
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};
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}
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