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comparison +rv/+time/RungekuttaExteriorRvBdf.m @ 1029:dce08a74e0ad feature/advectionRV

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Create a separate class of RungekuttaExteriorRV which uses BDFs for computing the time derivative. Remove BDFs from RungekuttaExteriorRV
author Vidar Stiernström <vidar.stiernstrom@it.uu.se>
date Fri, 11 Jan 2019 15:47:10 +0100
parents
children 2ef20d00b386
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equal deleted inserted replaced
1028:5df155ededcd 1029:dce08a74e0ad
1 classdef RungekuttaExteriorRvBdf < time.Timestepper
2 properties
3 F % RHS of the ODE
4 k % Time step
5 t % Time point
6 v % Solution vector
7 n % Time level
8 coeffs % The coefficents used for the RK time integration
9
10 % Properties related to the residual viscositys
11 RV % Residual Viscosity operator
12 viscosity % Viscosity vector
13 v_prev % Solution vector at previous time levels, used for the RV evaluation
14 DvDt % Function for computing the time deriative used for the RV evaluation
15 lowerBdfOrder % Orders of the approximation of the time deriative, used for the RV evaluation.
16 % dictates which accuracy the boot-strapping should start from.
17 upperBdfOrder % Orders of the approximation of the time deriative, used for the RV evaluation.
18 % Dictates the order of accuracy used once the boot-strapping is complete.
19
20 % Convenience properties. Only for plotting
21 residual
22 dvdt
23 Df
24 end
25 methods
26 function obj = RungekuttaExteriorRvBdf(F, k, t0, v0, RV, rkOrder, bdfOrders)
27 obj.F = F;
28 obj.k = k;
29 obj.t = t0;
30 obj.v = v0;
31 obj.n = 0;
32 % Extract the coefficients for the specified rkOrder
33 % used for the RK updates from the Butcher tableua.
34 [s,a,b,c] = time.rk.butcherTableau(rkOrder);
35 obj.coeffs = struct('s',s,'a',a,'b',b,'c',c);
36
37 obj.RV = RV;
38 % TBD: Decide on if the initialization of the previous stages used by
39 % the BDF should be done here, or if it should be checked for each
40 % step taken.
41 % If it is moved here, then multiple branching stages can be removed in step()
42 % but this will effectively result in a plotted simulation starting from n = upperBdfOrder.
43 % In addition, the properties lowerBdfOrder and upperBdfOrder can be removed.
44 obj.lowerBdfOrder = bdfOrders.lowerBdfOrder;
45 obj.upperBdfOrder = bdfOrders.upperBdfOrder;
46 assert((obj.lowerBdfOrder >= 1) && (obj.upperBdfOrder <= 6));
47 obj.v_prev = [];
48 obj.DvDt = rv.time.BdfDerivative();
49 obj.viscosity = zeros(size(v0));
50 obj.residual = zeros(size(v0));
51 obj.dvdt = zeros(size(v0));
52 obj.Df = zeros(size(v0));
53 end
54
55 function [v, t] = getV(obj)
56 v = obj.v;
57 t = obj.t;
58 end
59
60 function state = getState(obj)
61 state = struct('v', obj.v, 'residual', obj.residual, 'dvdt', obj.dvdt, 'Df', obj.Df, 'viscosity', obj.viscosity, 't', obj.t);
62 end
63
64 function obj = step(obj)
65 % Store current time level and update v_prev
66 numStoredStages = size(obj.v_prev,2);
67 if (numStoredStages < obj.upperBdfOrder)
68 obj.v_prev = [obj.v, obj.v_prev];
69 numStoredStages = numStoredStages+1;
70 else
71 obj.v_prev(:,2:end) = obj.v_prev(:,1:end-1);
72 obj.v_prev(:,1) = obj.v;
73 end
74
75 % Fix the viscosity of the RHS function F
76 F_visc = @(v,t) obj.F(v,t,obj.viscosity);
77 obj.v = time.rk.rungekutta(obj.v, obj.t, obj.k, F_visc, obj.coeffs);
78 obj.t = obj.t + obj.k;
79 obj.n = obj.n + 1;
80
81 %Calculate dvdt and evaluate RV for the new time level
82 if ((numStoredStages >= obj.lowerBdfOrder) && (numStoredStages <= obj.upperBdfOrder))
83 obj.dvdt = obj.DvDt.evaluate(obj.v, obj.v_prev, obj.k);
84 [obj.viscosity, obj.Df] = obj.RV.evaluate(obj.v,obj.dvdt);
85 obj.residual = obj.dvdt + obj.Df;
86 end
87 end
88 end
89 end