ode45 in GUI

Hi I am new to GUI and I want to solve odes in the GUI. But now there are some errors.

        function dhdt = toSolve(t,y)
            dhdt(1) = 5;
            dhdt(2) = 3;
            dhdt = dhdt';
        end

        function Button_2Pushed(app, event)
            [app.t, app.height_Tank1] = ode45(@toSolve,[0 20],[1; 3]);

            plot(app.UIAxes3, app.t, app.height_Tank1(:,1));
            app.UIAxes3.XLim = [0 20];
            app.UIAxes3.YLim = [-3 3];

            plot(app.UIAxes4, app.t, app.height_Tank1(:,2));
            app.UIAxes4.XLim = [0 20];
            app.UIAxes4.YLim = [-3 3];

        end

I wanted the second function to make use of the first function, vdp to solve ode. I realize that vdp could not be handled(referenced? not sure about the wording). The error message is "Undefined function 'toSolve.vdp' for input arguments of type 'double'.

Error in odearguments (line 90) f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115) odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);"

Could anyone help me with it? Thanks a lot!

[Walter Roberson]

? I do not see any vdp in the code ?