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annotate +rv/+time/RungeKuttaRvInstage.m @ 1181:9ac86ccfd6a1 feature/rv

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Move instage rungekutta time stepping to RungekuttaRvInstage
author Vidar Stiernström <vidar.stiernstrom@it.uu.se>
date Fri, 05 Jul 2019 16:51:05 +0200
parents d02e5b8a0b24
children
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d02e5b8a0b24 Rename RungekuttaRV time steppers. Add RungekuttaRVMultiStage time stepper
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1 classdef RungekuttaRvInstage < 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 coeffs % The coefficents used for the RK time integration
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9 RV % Residual Viscosity
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2ef20d00b386 For easier comparison, return both the first order and residual viscosity when evaluating the residual. Add the first order and residual viscosity to the state of the RungekuttaRV time steppers
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10 DvDt % Function for computing the time deriative used for the RV evaluation
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11 end
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12
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13 methods
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d02e5b8a0b24 Rename RungekuttaRV time steppers. Add RungekuttaRVMultiStage time stepper
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14 function obj = RungekuttaRvInstage(F, k, t0, v0, RV, DvDt, order)
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15 obj.F = F;
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16 obj.k = k;
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17 obj.t = t0;
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18 obj.v = v0;
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19 obj.n = 0;
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20 % Extract the coefficients for the specified order
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21 % used for the RK updates from the Butcher tableua.
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22 [s,a,b,c] = time.rk.butcherTableau(order);
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23 obj.coeffs = struct('s',s,'a',a,'b',b,'c',c);
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24 obj.RV = RV;
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25 obj.DvDt = DvDt;
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26 end
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27
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28 function [v, t] = getV(obj)
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29 v = obj.v;
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30 t = obj.t;
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31 end
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32
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33 function state = getState(obj)
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34 dvdt = obj.DvDt(obj.v);
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35 [viscosity, Df, firstOrderViscosity, residualViscosity] = obj.RV.evaluate(obj.v, dvdt);
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36 state = struct('v', obj.v, 'dvdt', dvdt, 'Df', Df, 'viscosity', viscosity, 'residualViscosity', residualViscosity, 'firstOrderViscosity', firstOrderViscosity, 't', obj.t);
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37 end
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38
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39 % Advances the solution vector one time step using the Runge-Kutta method given by
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40 % obj.coeffs, updating the Residual Viscosity in each Runge-Kutta stage
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41 function obj = step(obj)
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42 obj.v = rv.time.rungekuttaRV(obj.v, obj.t, obj.k, obj.F, obj.RV, obj.DvDt, obj.coeffs);
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43 obj.t = obj.t + obj.k;
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44 obj.n = obj.n + 1;
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45 end
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46 end
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47
9ac86ccfd6a1 Move instage rungekutta time stepping to RungekuttaRvInstage
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48 % Takes one time step of size dt using the rungekutta method
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49 % starting from v and where the function F(v,t,RV) gives the
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50 % time derivatives. coeffs is a struct holding the RK coefficients
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51 % for the specific method. RV is the residual viscosity which is updated
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52 % in between the stages and after the updated solution is computed.
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53 methods (Static)
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54 function v = rungekuttaRV(v, t , dt, F, RV, DvDt, coeffs)
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55 % Move one stage outside to avoid branching for updating the
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56 % residual inside the loop.
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57 k = zeros(length(v), coeffs.s);
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58 k(:,1) = F(v,t,RV.evaluateViscosity(v,DvDt(v)));
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59
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60 % Compute the intermediate stages k
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61 for i = 2:coeffs.s
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62 u = v;
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63 for j = 1:i-1
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64 u = u + dt*coeffs.a(i,j)*k(:,j);
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65 end
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66 k(:,i) = F(u,t+coeffs.c(i)*dt, RV.evaluateViscosity(u,DvDt(u)));
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67 end
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68
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69 % Compute the updated solution as a linear combination
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70 % of the intermediate stages.
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71 u = v;
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72 for i = 1:coeffs.s
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73 u = u + dt*coeffs.b(i)*k(:,i);
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74 end
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75 v = u;
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76 end
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79 end