Plotting on the axes with freqs() not working

Hello,so I'm basically working on a GUI with App Designer and the buttons work,but when I hit the Calculate button it doesn't plot on the FreqAxes.I have to use the freqs() function.

Here's the full code,I have no idea where I made a mistake,I'm beginner in Matlab and I learn it in University. (this is an univeristy project)

classdef matlab_app < matlab.apps.AppBase
    % Properties that correspond to app components
    properties (Access = public)
        UIFigure              matlab.ui.Figure
        KEdit                 matlab.ui.control.NumericEditField
        KEditEditFieldLabel   matlab.ui.control.Label
        PEdit                 matlab.ui.control.NumericEditField
        PEditEditFieldLabel   matlab.ui.control.Label
        APEdit                matlab.ui.control.NumericEditField
        APEditEditFieldLabel  matlab.ui.control.Label
        Calculate             matlab.ui.control.Button
        BEdit                 matlab.ui.control.NumericEditField
        BEditLabel            matlab.ui.control.Label
        ZPEdit                matlab.ui.control.NumericEditField
        ZPEditLabel           matlab.ui.control.Label
        FilterTypeGroup       matlab.ui.container.ButtonGroup
        StopRadio             matlab.ui.control.RadioButton
        HighRadio             matlab.ui.control.RadioButton
        BandpassRadio         matlab.ui.control.RadioButton
        LowRadio              matlab.ui.control.RadioButton
        WoEditField           matlab.ui.control.NumericEditField
        WoEditFieldLabel      matlab.ui.control.Label
        OrderSpinner          matlab.ui.control.Spinner
        OrderSpinnerLabel     matlab.ui.control.Label
        SyntaxListBox         matlab.ui.control.ListBox
        FreqAxes              matlab.ui.control.UIAxes
    end
    
    properties (Access = private)
        b
        a
        z
        p
        k 
        n double
        Wo
        filterType
        % Description
    end
    
    methods (Access = private)
        
        % Setting the right ftype
        function filterType = getFilterType(app)
            if app.LowRadio.Value
                filterType = 'low';
            elseif app.BandpassRadio.Value
                filterType = 'bandpass';
            elseif app.HighRadio.Value
                filterType = 'high';
            elseif app.StopRadio.Value
                filterType = 'stop';
            else
                filterType = ''; 
            end
        end
        
        % Buttons reset
        function resetControls(app)
            app.ZPEdit.Enable = 'off';
            app.APEdit.Enable = 'off';
            app.BEdit.Enable = 'off';
            app.PEdit.Enable = 'off';
            app.KEdit.Enable = 'off';
        end
        %{
        function plotFrequencyResponse(freq_response)
                figure;
                semilogx(freq_response(:,1), 20*log10(abs(freq_response(:,2))));
                title('Frequency Response');
                xlabel('Frequency (Hz)');
                ylabel('Magnitude (dB)');
                grid on;
        end
        %}
    end
    % Callbacks that handle component events
    methods (Access = private)
        % Value changed function: SyntaxListBox
        function SyntaxListBoxValueChanged(app, event)
            value = app.SyntaxListBox.Value;
            app.resetControls();
            switch value
                case 'besself (b, a)'
                    app.APEdit.Enable = 'on';
                    app.BEdit.Enable = 'on';
                case 'besself (z, p, k)'
                    app.ZPEdit.Enable = 'on';
                    app.PEdit.Enable = 'on';
                    app.KEdit.Enable = 'on';
                case 'besselap (z, p, k)'
                    app.ZPEdit.Enable = 'on';
                    app.PEdit.Enable = 'on';
                    app.KEdit.Enable = 'on';
            end
        end
        % Button pushed function: Calculate
        function CalculateButtonPushed(app, event)
            app.n = app.OrderSpinner.Value;
            app.Wo = str2double(app.WoEditField.Value);
            
            switch app.SyntaxListBox.Value
                case 'besself (b, a)'
                    %if isfinite(app.Wo)  % Check if Wo is finite
                    [app.b, app.a] = besself(round(app.n), app.Wo, app.getFilterType());
                    app.BEdit.Value = mat2str(app.b);
                    app.APEdit.Value = mat2str(app.a);
                    freq_response = freqs(app.b, app.a);
                    plot(app.FreqAxes, freq_response(:,1), 20*log10(abs(freq_response(:,2))));
                    %else
                    %   disp('Error: Wo should be a finite value.');
                    %end
                case 'besself (z, p, k)'
                    %if isfinite(app.Wo)
                    [app.z, app.p, app.k] = besself(round(app.n), app.Wo, app.getFilterType());
                    app.ZPEdit.Value = mat2str(app.z);
                    app.PEdit.Value = mat2str(app.p);
                    app.KEdit.Value = mat2str(app.k);
                    freq_response = freqs(app.z, app.p, app.k);
                    plot(app.FreqAxes, freq_response(:,1), 20*log10(abs(freq_response(:,2))));
                    %else
                    %   disp('Error: Wo should be a finite value.');
                    %end
                case 'besselap (z, p, k)'
                    %if isfinite(app.Wo)
                    [app.z, app.p, app.k] = besself(round(app.n), app.Wo, app.getFilterType());
                    app.ZPEdit.Value = mat2str(app.z);
                    app.PEdit.Value = mat2str(app.p);
                    app.KEdit.Value = mat2str(app.k);
                    freq_response = freqs(app.z, app.p, app.k);
                    plot(app.FreqAxes, freq_response(:,1), 20*log10(abs(freq_response(:,2))));
                    %else
                    %   disp('Error: Wo should be a finite value.');
                    %end
            end
            %{
            Plotting using freqs()
            freqsAxes = app.FreqAxes;
            freqsAxes.XLabel.String = 'Frequence (Hz)';
            freqsAxes.YLabel.String = 'Magnitude';
            [H, W] = freqs(app.b, app.a);
            plot(freqsAxes, W, abs(H));
            %}
            
        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 = [100 100 640 480];
            app.UIFigure.Name = 'MATLAB App';
            % Create FreqAxes
            app.FreqAxes = uiaxes(app.UIFigure);
            title(app.FreqAxes, 'FreqAxes')
            xlabel(app.FreqAxes, 'X')
            ylabel(app.FreqAxes, 'Y')
            zlabel(app.FreqAxes, 'Z')
            app.FreqAxes.FontAngle = 'italic';
            app.FreqAxes.FontWeight = 'bold';
            app.FreqAxes.Color = [1 1 0.0667];
            app.FreqAxes.XGrid = 'on';
            app.FreqAxes.YGrid = 'on';
            app.FreqAxes.Position = [18 197 404 256];
            % Create SyntaxListBox
            app.SyntaxListBox = uilistbox(app.UIFigure);
            app.SyntaxListBox.Items = {'besself (b, a)', 'besself (z, p, k)', 'besselap(z, p, k)'};
            app.SyntaxListBox.ValueChangedFcn = createCallbackFcn(app, @SyntaxListBoxValueChanged, true);
            app.SyntaxListBox.Position = [483 363 100 74];
            app.SyntaxListBox.Value = 'besself (b, a)';
            % Create OrderSpinnerLabel
            app.OrderSpinnerLabel = uilabel(app.UIFigure);
            app.OrderSpinnerLabel.HorizontalAlignment = 'right';
            app.OrderSpinnerLabel.Position = [26 113 77 22];
            app.OrderSpinnerLabel.Text = 'OrderSpinner';
            % Create OrderSpinner
            app.OrderSpinner = uispinner(app.UIFigure);
            app.OrderSpinner.Position = [118 113 100 22];
            % Create WoEditFieldLabel
            app.WoEditFieldLabel = uilabel(app.UIFigure);
            app.WoEditFieldLabel.HorizontalAlignment = 'right';
            app.WoEditFieldLabel.Position = [30 65 69 22];
            app.WoEditFieldLabel.Text = 'WoEditField';
            % Create WoEditField
            app.WoEditField = uieditfield(app.UIFigure, 'numeric');
            app.WoEditField.Position = [114 65 100 22];
            % Create FilterTypeGroup
            app.FilterTypeGroup = uibuttongroup(app.UIFigure);
            app.FilterTypeGroup.TitlePosition = 'centertop';
            app.FilterTypeGroup.Title = 'Filter Types';
            app.FilterTypeGroup.Position = [471 226 123 106];
            % Create LowRadio
            app.LowRadio = uiradiobutton(app.FilterTypeGroup);
            app.LowRadio.Text = 'low';
            app.LowRadio.Position = [11 66 41 22];
            app.LowRadio.Value = true;
            % Create BandpassRadio
            app.BandpassRadio = uiradiobutton(app.FilterTypeGroup);
            app.BandpassRadio.Text = 'bandpass';
            app.BandpassRadio.Position = [11 45 75 22];
            % Create HighRadio
            app.HighRadio = uiradiobutton(app.FilterTypeGroup);
            app.HighRadio.Text = 'high';
            app.HighRadio.Position = [11 21 45 22];
            % Create StopRadio
            app.StopRadio = uiradiobutton(app.FilterTypeGroup);
            app.StopRadio.Text = 'stop';
            app.StopRadio.Position = [11 1 46 22];
            % Create ZPEditLabel
            app.ZPEditLabel = uilabel(app.UIFigure);
            app.ZPEditLabel.HorizontalAlignment = 'right';
            app.ZPEditLabel.Position = [279 113 41 22];
            app.ZPEditLabel.Text = 'ZPEdit';
            % Create ZPEdit
            app.ZPEdit = uieditfield(app.UIFigure, 'numeric');
            app.ZPEdit.Position = [335 113 100 22];
            % Create BEditLabel
            app.BEditLabel = uilabel(app.UIFigure);
            app.BEditLabel.HorizontalAlignment = 'right';
            app.BEditLabel.Position = [286 24 34 22];
            app.BEditLabel.Text = 'BEdit';
            % Create BEdit
            app.BEdit = uieditfield(app.UIFigure, 'numeric');
            app.BEdit.Position = [335 24 100 22];
            % Create Calculate
            app.Calculate = uibutton(app.UIFigure, 'push');
            app.Calculate.ButtonPushedFcn = createCallbackFcn(app, @CalculateButtonPushed, true);
            app.Calculate.Position = [483 175 100 23];
            app.Calculate.Text = 'Calculate';
            % Create APEditEditFieldLabel
            app.APEditEditFieldLabel = uilabel(app.UIFigure);
            app.APEditEditFieldLabel.HorizontalAlignment = 'right';
            app.APEditEditFieldLabel.Position = [279 65 41 22];
            app.APEditEditFieldLabel.Text = 'APEdit';
            % Create APEdit
            app.APEdit = uieditfield(app.UIFigure, 'numeric');
            app.APEdit.Position = [335 65 100 22];
            % Create PEditEditFieldLabel
            app.PEditEditFieldLabel = uilabel(app.UIFigure);
            app.PEditEditFieldLabel.HorizontalAlignment = 'right';
            app.PEditEditFieldLabel.Position = [473 65 34 22];
            app.PEditEditFieldLabel.Text = 'PEdit';
            % Create PEdit
            app.PEdit = uieditfield(app.UIFigure, 'numeric');
            app.PEdit.Position = [522 65 100 22];
            % Create KEditEditFieldLabel
            app.KEditEditFieldLabel = uilabel(app.UIFigure);
            app.KEditEditFieldLabel.HorizontalAlignment = 'right';
            app.KEditEditFieldLabel.Position = [473 113 34 22];
            app.KEditEditFieldLabel.Text = 'KEdit';
            % Create KEdit
            app.KEdit = uieditfield(app.UIFigure, 'numeric');
            app.KEdit.Position = [522 113 100 22];
            % 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 = matlab_app
            % 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

[Voss]

• The outputs of freqs are described in the documentation here. Note that the first output is the frequency response (a vector) and the second output is the angular frequencies (also a vector). Use both outputs to be able to plot properly. (The documentation does not mention a situation where the first output is an m-by-2 matrix, which is apparently what you are expecting.)
• freqs does not take z,p,k inputs, only b,a inputs, so you must convert the z,p,k you get from besself with 3 outputs to b,a somehow, e.g., using zp2tf.
• The cases for 'besself (z, p, k)' and 'besselap (z, p, k)' are identical; they can be combined (like in the code below) or one option can be removed. I don't know what the intent is with that.

With those things in mind, your CalculateButtonPushed function might look something like this:

% Button pushed function: Calculate
function CalculateButtonPushed(app, event)

    app.n = app.OrderSpinner.Value;
    app.Wo = str2double(app.WoEditField.Value);
    
    switch app.SyntaxListBox.Value
        case 'besself (b, a)'
            %if isfinite(app.Wo)  % Check if Wo is finite
                [app.b, app.a] = besself(round(app.n), app.Wo, app.getFilterType());
            %else
             %   disp('Error: Wo should be a finite value.');
            %end
        case {'besself (z, p, k)','besselap (z, p, k)'}
            %if isfinite(app.Wo)
                [app.z, app.p, app.k] = besself(round(app.n), app.Wo, app.getFilterType());
                app.ZPEdit.Value = mat2str(app.z);
                app.PEdit.Value = mat2str(app.p);
                app.KEdit.Value = mat2str(app.k);
                [app.b, app.a] = zp2tf(app.z, app.p, app.k);
            %else
             %   disp('Error: Wo should be a finite value.');
            %end
    end
    
    app.BEdit.Value = mat2str(app.b);
    app.APEdit.Value = mat2str(app.a);
    
    [freq_response, w] = freqs(app.b, app.a);
    plot(app.FreqAxes, w, 20*log10(abs(freq_response)));
    
end

[MOLNAR]

Thank you very much! It kinda solved my problem,but when I try to run besselap it doesn't draw anything on axes and it only displays null vectors.Should it be like this?

And i have some buttons to choose the filter type,how do I do if i pick bandpass or stop?It says I need a vector or smth and I have no idea how to solve this.

[Voss]

You're welcome!

According to the documentation besselap is only for lowpass filters.

https://www.mathworks.com/help/signal/ref/besselap.html