Change intensity of zplane figure

Hello everyone,

I was trying to change the line-width of the zplane figure in order to make it more visible.I tried the set command but it didnt work.How can i fix it so it can work?

Thanks in advance.

This is my code so far:

function Lab2_Part_One
    close all;
    clearvars;

    % Create directory if it doesn't exist
    directory = 'Ask1';
    if ~isfolder(directory) %For versions before R2017b use exist 
                            % instead of is folder
        mkdir(directory);
    end

    % Given transfer function
    num = [0.2 0]; % Numerator coefficients
    den = [1 -0.7 -0.18]; % Denominator coefficients
    w = -pi:pi/128:pi; % Frequency range

    % Function calls
    plotPoleZeroPlot(num, den, directory);
end

function plotPoleZeroPlot(num, den, directory)
    % Function to plot the pole-zero plot
    figure;
    h = zplane(num, den);

% Set the properties for poles (red lines)
set(h_poles, 'Color', 'green', 'LineWidth', 2); % Change color to green and line width

% Set the properties for zeros (blue lines)
set(h_zeros, 'Color', 'magenta', 'LineWidth', 1.5); % Change color to magenta and line width

% Redraw the unit circle with the desired linewidth
hold on;
t = 0:0.01:2 * pi; % Define points for the unit circle
plot(cos(t), sin(t), 'Color', [0 0.4470 0.7410], 'LineWidth', 1); % Plot the unit circle with the desired linewidth
    %grid on;
    title('Pole-Zero Plot of the Transfer Function H(z)');

    % Save the pole-zero plot in the specified directory as a PNG file
    filename = fullfile(directory, 'pole_zero_plot.png');
    saveas(gcf, filename);
end

Answer 1

[Star Strider]

Changing the properties requirees a bit of handle-spelunking, however it is possible.

Try this —

[z,p,k] = ellip(4,3,30,200/500);

figure
zplane(z,p)
grid
title('4th-Order Elliptic Lowpass Digital Filter')

figure
hzp = zplane(z,p);
grid
title('4th-Order Elliptic Lowpass Digital Filter')

getgca = get(gca);
Kids = getgca.Children;
Kids(2).Color = 'g';
Kids(2).LineWidth = 2;
Kids(3).Color = 'm';
Kids(3).LineWidth = 1.5;

% figure
% hold on
% plot(Kids(1).XData, Kids(1).YData, ':')
% plot(Kids(2).XData, Kids(2).YData, 'xg', 'LineWidth',2)
% plot(Kids(3).XData, Kids(3).YData, 'om', 'LineWidth',1.5)
% hold off
% axis([[-1 1]*1.5  [-1 1]*1.25])
% grid

The zplane function creates 3 different line objects, and once they are found, changing their properties is straightforward.

.

[Konstantinos]

Thanks a lot

[Star Strider]

As always, my pleasure!

Additionally:

Kids(1): Unit Circle

Kids(2): Poles

Kids(3): Zeros

These are each line objects with their own properties. That should hold for all recent releases.

.

[Konstantinos]

Well this is not always the case.When i use the zplane(b,a) where b and a are the numerator and denominator coefficients already defined by the user the unit circle and the zeros are "connected" and i dont know why.But when i use the zplace(d,g) with:

d = roots(numerator)
g = roots(denominator)

it works fine.

This image is without the use of function root:

The image above is generated by using the function roots.

Also in the second image the number 2 is disappearing.

[Star Strider]

So much for consistency. I was hoping that ordering would always work, It doesn’t.

So, Plan ‘B’ —

num = [0.2 0]; % Numerator coefficients
den = [1 -0.7 -0.18]; % Denominator coefficients

figure
zplane(num, den)

getgca = get(gca);
Kids = getgca.Children;
% Number = findobj(Kids','Type','text')
Lines = findobj(Kids, 'Type','line');
for k = 1:numel(Lines)                                  % Match Markers To 'Lines' Indices
    if strcmp(Lines(k).Marker, 'x')
        Poles = k;
    elseif strcmp(Lines(k).Marker, 'o')
        Zeros = k;
    elseif strcmp(Lines(k).Marker, 'none')
        UnitCircle = k;
    end
end
% Poles
% Zeros
% UnitCircle

Lines(Poles).Color = 'g';
Lines(Poles).LineWidth = 2;
Lines(Zeros).Color = 'm';
Lines(Zeros).LineWidth = 1.5;

This looks up the markers, saves the appropriate indices, and then does the appropriate assignments. You can change the ‘UnitCircle’ properties as well, if you want to. The same syntax works.

The ‘2’ is a separate text object. (This can be seen by removing the semicolon from the end of the ‘Kids’ assignment.) You would have to add that to your plot using roots. It always appears to be the first entry, so you can either refer to it as ‘Kids(1)’ or do:

Number = findobj(Kids','Type','text')

I added it (to be certain that it does what I want it to do) and then commented it out. Un-comment it to explore its properties to see how that text call works.

.

[Konstantinos]

Nice solution.

I tried this instead which is based on your first comment.

num = [0.2 0]; % Numerator coefficients
den = [1 -0.7 -0.18]; % Denominator coefficients

plotPoleZeroPlot(num, den);

function plotPoleZeroPlot(num, den)
    % Function to plot the pole-zero plot
    figure;

    % Obtain zeros and poles of the system
    zeros_of_system = roots(num); % Zeros
    poles_of_system = roots(den); % Poles

    % Plot pole-zero plot
    zplane(zeros_of_system, poles_of_system );

    % Customize plot appearance
    getgca = get(gca); %Returns the current axes.
    Kids = getgca.Children;
    Kids(1).Color = [0 0.4470 0.7410];
    Kids(1).LineWidth = 2;
    Kids(2).Color = 'r';
    Kids(2).LineWidth = 2;
    Kids(3).Color = 'r';
    Kids(3).LineWidth = 2;

    % Add title and grid to the plot
    title('Pole-Zero Plot of the Transfer Function H(z)');
    grid on;
end

It seems a little bit easier and less complex.

[Star Strider]

Thank you!

It is easier, however it appears that the line objects do not always appear in the same order, for whatever reason. If you want them to all be the same colours and sizes, the first solution is easier. If you want them to be specifically different, the strcmp approach is necessary. It all depends on what you want.

[Konstantinos]

Thanks.I will keep in mind