classdef Rungekutta < time.Timestepper
    properties
        F       % RHS of the ODE
        k       % Time step
        t       % Time point
        v       % Solution vector
        n       % Time level
        scheme  % The scheme used for the time stepping, e.g rk4, rk6 etc.
    end


    methods
        % Timesteps v_t = F(v,t), using the specified RK method from t = t0 with
        % timestep k and initial conditions v = v0
        function obj = Rungekutta(F, k, t0, v0, method)
            default_arg('method',"rk4");
            obj.F = F;
            obj.k = k;
            obj.t = t0;
            obj.v = v0;
            obj.n = 0;
            % TODO: method "rk4" is also implemented in the butcher tableau, but the rungekutta_4.m implementation
            % might be slightly more efficient. Need to do some profiling before deciding whether or not to keep it.
            if (method == "rk4")
                obj.scheme = @time.rk.rungekutta_4;
            else
                % Extract the coefficients for the specified method
                % used for the RK updates from the Butcher tableua.
                [s,a,b,c] = time.rk.butcherTableau(method);
                coeffs = struct('s',s,'a',a,'b',b,'c',c);
                obj.scheme = @(v,t,dt,F) time.rk.rungekutta(v, t , dt, F, coeffs);
            end
        end

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

        function obj = step(obj)
            obj.v = obj.scheme(obj.v, obj.t, obj.k, obj.F);
            obj.t = obj.t + obj.k;
            obj.n = obj.n + 1;
        end
    end
end