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annotate +time/Rungekutta.m @ 888:8732d6bd9890 feature/timesteppers

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Add general Runge-Kutta class - Add a general Runge-Kutta class which time integrates the solution based on coefficients obtained from a Butcher tableau - Add butcher tableau which returns coefficents for the specified Runge-Kutta method - Remove RungKutta4proper, since obsolete
author Vidar Stiernström <vidar.stiernstrom@it.uu.se>
date Thu, 15 Nov 2018 17:10:01 -0800
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children 679f4ddd982f
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1 classdef Rungekutta < time.Timestepper
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2 properties
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3 F % RHS of the ODE
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4 k % Time step
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5 t % Time point
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6 v % Solution vector
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7 n % Time level
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8 scheme % The scheme used for the time stepping, e.g rk4, rk6 etc.
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9 end
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10
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11
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12 methods
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13 % Timesteps v_t = F(v,t), using the specified RK method from t = t0 with
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14 % timestep k and initial conditions v = v0
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15 function obj = Rungekutta(F, k, t0, v0, method)
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16 default_arg('method',"rk4");
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17 obj.F = F;
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18 obj.k = k;
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19 obj.t = t0;
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20 obj.v = v0;
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21 obj.n = 0;
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22 % TODO: method "rk4" is also implemented in the butcher tableau, but the rungekutta_4.m implementation
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23 % might be slightly more efficient. Need to do some profiling before deciding whether or not to keep it.
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24 if (method == "rk4")
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25 obj.scheme = @time.rk.rungekutta_4;
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26 else
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27 % Extract the coefficients for the specified method
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28 % used for the RK updates from the Butcher tableua.
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29 [s,a,b,c] = time.rk.butcherTableau(method);
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30 coeffs = struct('s',s,'a',a,'b',b,'c',c);
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31 obj.scheme = @(v,t,dt,F) time.rk.rungekutta(v, t , dt, F, coeffs);
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32 end
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33 end
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34
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35 function [v,t] = getV(obj)
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36 v = obj.v;
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37 t = obj.t;
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38 end
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39
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40 function obj = step(obj)
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41 obj.v = obj.scheme(obj.v, obj.t, obj.k, obj.F);
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42 obj.t = obj.t + obj.k;
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43 obj.n = obj.n + 1;
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44 end
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45 end
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46 end