classdef Rungekutta < time.Timestepper
    properties
        F       % RHS of the ODE
        k       % Time step
        t       % Time point
        v       % Solution vector
        n       % Time level
        coeffs  % The coefficents used for the RK time integration
    end


    methods
        % Timesteps v_t = F(v,t), using RK with specfied order from t = t0 with
        % timestep k and initial conditions v = v0
        function obj = Rungekutta(F, k, t0, v0, order)
            default_arg('order',4);
            obj.F = F;
            obj.k = k;
            obj.t = t0;
            obj.v = v0;
            obj.n = 0;
            % Extract the coefficients for the specified order
            % used for the RK updates from the Butcher tableua.
            [s,a,b,c] = butcherTableau(order);
            obj.coeffs = struct('s',s,'a',a,'b',b,'c',c);
        end

        function [v,t] = getV(obj)
            v = obj.v;
            t = obj.t;
        end

        function obj = step(obj)
            obj.v = time.rk.rungekutta(obj.v, obj.t, obj.k, obj.F, obj.coeffs);
            obj.t = obj.t + obj.k;
            obj.n = obj.n + 1;
        end
    end
end