--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+time/ExplicitRungeKuttaDiscreteData.m	Thu Mar 10 16:54:26 2022 +0100
@@ -0,0 +1,121 @@
+classdef ExplicitRungeKuttaDiscreteData < time.Timestepper
+    properties
+        D
+        S           % Function handle for time-dependent data
+        data        % Matrix of data vectors, one column per stage
+        k
+        t
+        v
+        m
+        n
+        order
+        a, b, c, s  % Butcher tableau
+        K           % Stage rates
+        U           % Stage approximations
+        T           % Stage times
+    end
+
+
+    methods
+        function obj = ExplicitRungeKuttaDiscreteData(D, S, data, k, t0, v0, order)
+            default_arg('order', 4);
+            default_arg('S', []);
+            default_arg('data', []);
+
+            obj.D = D;
+            obj.S = S;
+            obj.k = k;
+            obj.t = t0;
+            obj.v = v0;
+            obj.m = length(v0);
+            obj.n = 0;
+            obj.order = order;
+            obj.data = data;
+
+            switch order
+            case 4
+                [obj.a, obj.b, obj.c, obj.s] = time.rkparameters.rk4();
+            otherwise
+                error('That RK method is not available');
+            end
+
+            obj.K = zeros(obj.m, obj.s);
+            obj.U = zeros(obj.m, obj.s);
+
+        end
+
+        function [v,t,U,T,K] = getV(obj)
+            v = obj.v;
+            t = obj.t;
+            U = obj.U; % Stage approximations in previous time step.
+            T = obj.T; % Stage times in previous time step.
+            K = obj.K; % Stage rates in previous time step.
+        end
+
+        function [a,b,c,s] = getTableau(obj)
+            a = obj.a;
+            b = obj.b;
+            c = obj.c;
+            s = obj.s;
+        end
+
+        % Returns quadrature weights for stages in one time step
+        function quadWeights = getTimeStepQuadrature(obj)
+            [~, b] = obj.getTableau();
+            quadWeights = obj.k*b;
+        end
+
+        function obj = step(obj)
+            v = obj.v;
+            a = obj.a;
+            b = obj.b;
+            c = obj.c;
+            s = obj.s;
+            S = obj.S;
+            dt = obj.k;
+            K = obj.K;
+            U = obj.U;
+            D = obj.D;
+            data = obj.data;
+
+            for i = 1:s
+                U(:,i) = v;
+                for j = 1:i-1
+                    U(:,i) = U(:,i) + dt*a(i,j)*K(:,j);
+                end
+
+                K(:,i) = D*U(:,i);
+                obj.T(i) = obj.t + c(i)*dt;
+
+                % Data from continuous function and discrete time-points.
+                if ~isempty(S)
+                    K(:,i) = K(:,i) + S(obj.T(i));
+                end
+                if ~isempty(data)
+                    K(:,i) = K(:,i) + data(:,obj.n*s + i);
+                end
+
+            end
+
+            obj.v = v + dt*K*b;
+            obj.t = obj.t + dt;
+            obj.n = obj.n + 1;
+            obj.U = U;
+            obj.K = K;
+        end
+    end
+
+
+    methods (Static)
+        function k = getTimeStep(lambda, order)
+            default_arg('order', 4);
+            switch order
+            case 4
+                k = time.rk4.get_rk4_time_step(lambda);
+            otherwise
+                error('Time-step function not available for this order');
+            end
+        end
+    end
+
+end
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