view +time/+rk/butcherTableau.m @ 1031:2ef20d00b386 feature/advectionRV

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
author Vidar Stiernström <vidar.stiernstrom@it.uu.se>
date Thu, 17 Jan 2019 10:25:06 +0100
parents e0560bc4fb7d
children
line wrap: on
line source

function [s,a,b,c] = butcherTableau(order)
% TODO: Change order from a double to string.
switch order
  
    case 3
        % TVD (Total Variational Diminishing)
        s = 3;
        a = zeros(s,s-1);
        a(2,1) = 1;
        a(3,1) = 1/4; a(3,2) = 1/4;
        b = [1/6, 1/6, 2/3];
        c = [0 1 1/2];
    case 4
        % Standard RK4
        s = 4;
        a = zeros(s,s-1);
        a(2,1) = 1/2; 
        a(3,1) = 0; a(3,2) = 1/2;
        a(4,1) = 0; a(4,2) = 0; a(4,3) = 1;
        b = [1/6 1/3 1/3 1/6];
        c = [0, 1/2, 1/2, 1];
    % case 4-3/8
    %     % 3/8 RK4 (Kuttas method). Lower truncation error, more flops
    %     s = 4;
    %     a = zeros(s,s-1);
    %     a(2,1) = 1/3; 
    %     a(3,1) = -1/3; a(3,2) = 1;
    %     a(4,1) = 1; a(4,2) = -1; a(4,3) = 1;
    %     b = [1/8 3/8 3/8 1/8];
    %     c = [0, 1/3, 2/3, 1];
    case 6
        % Runge-Kutta 6 from Alshina07 
        s = 7;
        a = zeros(s,s-1);
        a(2,1) = 4/7; 
        a(3,1) = 115/112; a(3,2) = -5/16;
        a(4,1) = 589/630; a(4,2) = 5/18; a(4,3) = -16/45;
        a(5,1) = 229/1200 - 29/6000*sqrt(5); a(5,2) = 119/240 - 187/1200*sqrt(5); a(5,3) = -14/75 + 34/375*sqrt(5); a(5,4) = -3/100*sqrt(5);
        a(6,1) = 71/2400 - 587/12000*sqrt(5); a(6,2) = 187/480 - 391/2400*sqrt(5); a(6,3) = -38/75 + 26/375*sqrt(5); a(6,4) = 27/80 - 3/400*sqrt(5); a(6,5) = (1+sqrt(5))/4;
        a(7,1) = -49/480 + 43/160*sqrt(5); a(7,2) = -425/96 + 51/32*sqrt(5); a(7,3) = 52/15 - 4/5*sqrt(5); a(7,4) = -27/16 + 3/16*sqrt(5); a(7,5) = 5/4 - 3/4*sqrt(5); a(7,6) = 5/2 - 1/2*sqrt(5);
        b = [1/12 0 0 0 5/12 5/12 1/12];
        c = [0, 4/7, 5/7, 6/7, (5-sqrt(5))/10, (5+sqrt(5))/10, 1];
    otherwise
        error('That Runge-Kutta order is not implemented', order)
        
end