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annotate +time/Rungekutta4SecondOrder.m @ 985:ad6de007e7f6 feature/timesteppers

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Convert Rungekutta4SecondOrder to take F(t,v,v_t) instead of matrices
author Jonatan Werpers <jonatan@werpers.com>
date Tue, 08 Jan 2019 12:34:29 +0100
parents 0585a2ee7ee7
children a99f00896b8e
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1 classdef Rungekutta4SecondOrder < time.Timestepper
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2 properties
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3 F
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4 dt
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5 t
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6 n
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7
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8 G % RHS for rewritten system
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9 w
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10 end
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13 methods
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14 % Create a time stepper for
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15 % v_tt = F(t,v,v_t), v(t0) = v0, v_t(t0) = v0t
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16 % with step size dt, by rewriting on first order form
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17 function obj = Rungekutta4SecondOrder(F, dt, t0, v0, v0t)
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18 obj.F = F;
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19 obj.dt = dt;
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20 obj.t = t0;
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21 obj.n = 0;
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22
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23 m = length(v0);
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24 obj.w = [v0; v0t];
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25 obj.G = @(t, w)[
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26 w(m+1:end);
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27 F(t,w(1:m), w(m+1:end));
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28 ];
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29 end
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30
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31 function [v,t] = getV(obj)
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32 v = obj.w(1:end/2);
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33 t = obj.t;
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34 end
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35
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36 function [vt,t] = getVt(obj)
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37 vt = obj.w(end/2+1:end);
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38 t = obj.t;
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39 end
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41 function obj = step(obj)
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42 % TODO: Avoid extra storage
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43 w = obj.w;
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44 dt = obj.dt;
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46 k1 = obj.G(t, w);
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47 k2 = obj.G(t + 0.5*dt, w + 0.5*dt*k1);
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48 k3 = obj.G(t + 0.5*dt, w + 0.5*dt*k2);
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49 k4 = obj.G(t + dt, w + dt*k3);
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51 obj.w = w + dt*(1/6)*(k1+2*(k2+k3)+k4);
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52 obj.t = obj.t + obj.dt;
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53 obj.n = obj.n + 1;
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54 end
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55 end
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58 methods (Static)
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59 function k = getTimeStep(lambda)
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60 k = rk4.get_rk4_time_step(lambda);
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61 end
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62 end
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64 end