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annotate +time/+rk/General.m @ 993:44e7e497c3b7 feature/timesteppers

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Make time.rk.General accept a butcher tableau instead of a string to choose method. String variant implemented as a static method
author Jonatan Werpers <jonatan@werpers.com>
date Wed, 09 Jan 2019 11:14:16 +0100
parents bbd165cc585c
children 10c5eda235b7
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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bbd165cc585c Move time.Rungekutta to time.rk.General
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1 classdef General < time.Timestepper
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2 properties
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3 F % RHS of the ODE
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4 dt % 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 coeffs % Butcher tableau coefficients
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10 V % All stage approximations in most recent time step
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11 K % All stage rates in most recent time step
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12 end
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13
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14
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15 methods
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16 % Timesteps v_t = F(v,t), using the specified ButcherTableau
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17 % from t = t0 with timestep dt and initial conditions v(0) = v0
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18 function obj = General(F, dt, t0, v0, bt, discreteData)
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19 assertType(bt, 'time.rk.ButcherTableau')
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20 default_arg('discreteData', []);
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21 obj.F = F;
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22 obj.dt = dt;
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23 obj.t = t0;
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24 obj.v = v0;
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25 obj.n = 0;
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26
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27 assert(bt.isExplicit())
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28 obj.coeffs = struct('s',bt.nStages,'a',bt.a(:,1:end-1),'b',bt.b,'c',bt.c);
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29
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30 if isempty(discreteData)
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31 obj.scheme = @(v,t,n) time.rk.rungekutta(v, t, dt, F, obj.coeffs);
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32 else
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33 obj.scheme = @(v,t,n) time.rk.rungekuttaDiscreteData(v, t, dt, F, obj.coeffs, discreteData, n);
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34 end
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35 end
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36
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37 % v: Current solution
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38 % t: Current time
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39 % V: All stage approximations in most recent time step
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40 % K: All stage rates in most recent time step
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41 % T: Time points (corresponding to V and K) in most recent time step
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42 function [v,t,V,T,K] = getV(obj)
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43 v = obj.v;
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44 t = obj.t;
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45 V = obj.V;
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46 K = obj.K;
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47 T = obj.t + obj.dt*obj.coeffs.b;
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48 end
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49
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50 function obj = step(obj)
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51 [obj.v, obj.V, obj.K] = obj.scheme(obj.v, obj.t, obj.n);
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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
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56 % Returns a vector of time points, including substage points,
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57 % in the time interval [t0, tEnd].
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58 % The time-step obj.dt is assumed to be aligned with [t0, tEnd] already.
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59 function tvec = timePoints(obj, t0, tEnd)
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60 N = round( (tEnd-t0)/obj.dt );
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61 tvec = zeros(N*obj.s, 1);
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62 s = obj.coeffs.s;
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63 c = obj.coeffs.c;
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64 for i = 1:N
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65 ind = (i-1)*s+1 : i*s;
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66 tvec(ind) = ((i-1) + c')*obj.dt;
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67 end
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68 end
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69
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70 % Returns a vector of quadrature weights corresponding to grid points
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71 % in time interval [t0, tEnd], substage points included.
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72 % The time-step obj.dt is assumed to be aligned with [t0, tEnd] already.
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73 function weights = quadWeights(obj, t0, tEnd)
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74 N = round( (tEnd-t0)/obj.dt );
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75 b = obj.coeffs.b;
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76 weights = repmat(b', N, 1);
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77 end
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78 end
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79
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80 methods(Static)
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81 % TBD: Function name
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82 function ts = methodFromStr(F, dt, t0, v0, methodStr, discreteData)
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83 default_arg('discreteData', []);
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84
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85 try
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86 bt = time.rk.ButcherTableau.(method);
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87 catch
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88 error('Runge-Kutta method ''%s'' is not implemented', methodStr)
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89 end
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90
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91 ts = time.rk.General(F, dt, t0, v0, bt, discreteData);
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92 end
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93 end
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94 end