How to use a slider's value as an index to plot a dot that moves in App Designer

Hi guys,

i'm new to App Designer and i want to plot two graphs and use one slider, to do so i wrote a code that basically plot both graphs (the first one is X and Y that are very long vectors, and the second one is r that is as long as the other two) when the PLOT button is pushed and then sets the limits of the 2 graphs. Then when i take the slider value and use it as a zoom in the x axis of the second graph, then i use the value of the slider as an index for plotting a single dot that should be moving along the first graph that should be already plotted.

Now, everything works fine, until it reaches the last line where there's an error that says "Array indices must be positive integers or logical values." so then i thought that it's the division that i do when calculating n so i rounded it as you all can see, but the error it's still there, please help me and also give me advices on how to get better at coding.

Thank you very much, R.

classdef app7 < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        UIFigure      matlab.ui.Figure
        Slider        matlab.ui.control.Slider
        SliderLabel   matlab.ui.control.Label
        YAWRATELabel  matlab.ui.control.Label
        TRACKLabel    matlab.ui.control.Label
        HOMEButton    matlab.ui.control.Button
        PLOTButton    matlab.ui.control.Button
        UIAxes2       matlab.ui.control.UIAxes
        UIAxes        matlab.ui.control.UIAxes
    end

    % Callbacks that handle component events
    methods (Access = private)

        % Button pushed function: HOMEButton
        function HOMEButtonPushed(app, event)
            delete(app.UIFigure);
        end

        % Button pushed function: PLOTButton
        function PLOTButtonPushed(app, event)
            X=evalin('base','X');
            Y=evalin('base','Y');
            r=evalin('base','yaw_rate');
            xlim(app.UIAxes, [min(X), max(X)]);
            ylim(app.UIAxes, [min(Y), max(Y)]);
            xlim(app.UIAxes2, [0, length(r)]);
            ylim(app.UIAxes2, [min(r), max(r)]);
            plot(app.UIAxes2, r); 
            plot(app.UIAxes,X,Y)
        end

        % Value changing function: Slider
        function SliderValueChanging(app, event)
            X=evalin('base','X');
            Y=evalin('base','Y');
            v = event.Value;
            n = length(X)*v/1000;
            round(n);
            xlim(app.UIAxes2, [n, 200+n]);
            plot(app.UIAxes, X(v), Y(v), '.', 'LineWidth',2);
        end
    end

    % Component initialization
    methods (Access = private)

        % Create UIFigure and components
        function createComponents(app)

            % Create UIFigure and hide until all components are created
            app.UIFigure = uifigure('Visible', 'off');
            app.UIFigure.Position = [100 100 852 600];
            app.UIFigure.Name = 'MATLAB App';

            % Create UIAxes
            app.UIAxes = uiaxes(app.UIFigure);
            title(app.UIAxes, 'Track')
            xlabel(app.UIAxes, 'X')
            ylabel(app.UIAxes, 'Y')
            zlabel(app.UIAxes, 'Z')
            app.UIAxes.Position = [1 256 853 345];

            % Create UIAxes2
            app.UIAxes2 = uiaxes(app.UIFigure);
            title(app.UIAxes2, 'Yaw Rate')
            ylabel(app.UIAxes2, 'rad/sec')
            zlabel(app.UIAxes2, 'Z')
            app.UIAxes2.Position = [1 1 441 256];

            % Create PLOTButton
            app.PLOTButton = uibutton(app.UIFigure, 'push');
            app.PLOTButton.ButtonPushedFcn = createCallbackFcn(app, @PLOTButtonPushed, true);
            app.PLOTButton.FontSize = 20;
            app.PLOTButton.Position = [469 185 96 50];
            app.PLOTButton.Text = 'PLOT';

            % Create HOMEButton
            app.HOMEButton = uibutton(app.UIFigure, 'push');
            app.HOMEButton.ButtonPushedFcn = createCallbackFcn(app, @HOMEButtonPushed, true);
            app.HOMEButton.FontSize = 20;
            app.HOMEButton.Position = [717 36 96 50];
            app.HOMEButton.Text = 'HOME';

            % Create TRACKLabel
            app.TRACKLabel = uilabel(app.UIFigure);
            app.TRACKLabel.HorizontalAlignment = 'center';
            app.TRACKLabel.FontSize = 20;
            app.TRACKLabel.FontWeight = 'bold';
            app.TRACKLabel.Position = [727 197 75 26];
            app.TRACKLabel.Text = 'TRACK';

            % Create YAWRATELabel
            app.YAWRATELabel = uilabel(app.UIFigure);
            app.YAWRATELabel.HorizontalAlignment = 'center';
            app.YAWRATELabel.FontSize = 20;
            app.YAWRATELabel.FontWeight = 'bold';
            app.YAWRATELabel.Position = [463 48 107 26];
            app.YAWRATELabel.Text = 'YAW RATE';

            % Create SliderLabel
            app.SliderLabel = uilabel(app.UIFigure);
            app.SliderLabel.HorizontalAlignment = 'right';
            app.SliderLabel.Position = [469 140 36 22];
            app.SliderLabel.Text = 'Slider';

            % Create Slider
            app.Slider = uislider(app.UIFigure);
            app.Slider.Limits = [0 1000];
            app.Slider.ValueChangingFcn = createCallbackFcn(app, @SliderValueChanging, true);
            app.Slider.Position = [526 149 260 3];

            % Show the figure after all components are created
            app.UIFigure.Visible = 'on';
        end
    end

    % App creation and deletion
    methods (Access = public)

        % Construct app
        function app = app7

            % Create UIFigure and components
            createComponents(app)

            % Register the app with App Designer
            registerApp(app, app.UIFigure)

            if nargout == 0
                clear app
            end
        end

        % Code that executes before app deletion
        function delete(app)

            % Delete UIFigure when app is deleted
            delete(app.UIFigure)
        end
    end
end

Answer 1

[Walter Roberson]

            round(n);

That has no effect, as you are not assigning the result to anything.

But it is unnecessary anyhow: you use n as the xlim and non-integer xlim is not a problem.

You should be doing

          v = round(v);

However... your slider limits are [0 1000] and you will have a problem when the slider is 0.

I suggest that you change the slider limits to [1 1000]

[Riccardo]

Thank you, that was very useful, but now when i move the slider it shows every dot that i do, how can i have only one dot moving along my first graph? Thank you again, R.

[Walter Roberson]

I do not see any reason in your posted code why it would draw multiple points. But I suspect that you must have turned hold on on the axes at some point: your current arrangement would remove the axes labels every time you plotted anything.