Change marker colour of pzplot

Hello everyone

I'm trying to change the marker color in the pzplot graph. I'm using version 2024b (edit:) and a LiveScript.

Apparently the code below works for a regular script, but doesn't work in a LiveScript. Maybe this is a rendering bug?

Apparently, in this version, a new object(?) called "PZPlot Properties" was introduced, which is great.

Using this new object, I can easily change the size and line thickness of all markers. But I can also only change the colour of all markers. I'd like to change the colours of the markers for the poles and zeros separately.

I tried using the "findobj" method and found, that the PZPlot apparently consists of two Scatter-Plots called "PZPoleScatter" and "PZZeroScatter", and I tried changing the color of the markers in those Scatter plots, but this does not seem to have an effect on the markers.

When I change the colour of the markers using the PZPlot properties Object, I see the color definition of the markers in both scatter plots change, and I can also see that the colours change if I directly access the properties and change the colour, but the plot isn't drawn with those correct colors.

I tried using refresh after changing the values, but that doesn't have any effect either.

See my code below:

s = tf('s');

f = (1 + 1/s)

pzp = pzplot(f);
% See https://ch.mathworks.com/help/ident/ref/controllib.chart.pzplot-properties.html for new PZPlot-properties object
pzp.Responses.MarkerSize = 10;
pzp.Responses.LineWidth = 2;
%pzp.Responses.Color = 'green'; % Changes colour of all markers
oPole = findobj(gca, 'Tag', 'PZPoleScatter');
oPole.MarkerEdgeColor = 'red';
oZero = findobj(gca, 'Tag', 'PZZeroScatter');
oZero.MarkerEdgeColor = 'blue';

rsp = findobj(gca, 'Tag', 'PZPoleScatter'); % read object again to see if properties got changed correctly

I also found the following two topics, but they do not work anymore as there is no "Line" child in the PZPlot object.

• https://ch.mathworks.com/matlabcentral/answers/276605-change-pzplot-marker-size
• https://ch.mathworks.com/matlabcentral/answers/431293-i-am-using-pole-zero-map-pzmap-and-i-want-to-enhance-the-size-of-pole-or-zero-or-in-other-words-i

[prabhat kumar sharma]

In MATLAB 2024b, you've encountered a situation where you want to change the colors of poles and zeros separately in a `pzplot`. With the introduction of new "PZPlot Properties," it seems the method to directly modify scatter plot properties has changed. Here's a way to tackle this:

Customizing Pole-Zero Plot Colors

To change the colors of poles and zeros separately, you can use the `PZPlot` properties and leverage the `findobj` method to locate specific plot elements. Here's how you can do it:

% Define the transfer function
s = tf('s');
f = (1 + 1/s);

% Create the pole-zero plot
pzp = pzplot(f);

% Customize the plot using PZPlot properties
pzp.Responses.MarkerSize = 10;
pzp.Responses.LineWidth = 2;

% Find the pole and zero scatter plot objects
oPole = findobj(pzp.AxesGrid, 'Tag', 'PZPoleScatter');

Unrecognized method, property, or field 'AxesGrid' for class 'controllib.chart.PZPlot'.

oZero = findobj(pzp.AxesGrid, 'Tag', 'PZZeroScatter');

% Check if the objects are found and then set their colors
if ~isempty(oPole)
    oPole.MarkerEdgeColor = 'red'; % Change pole color to red
end

if ~isempty(oZero)
    oZero.MarkerEdgeColor = 'blue'; % Change zero color to blue
end

% Refresh the plot to apply changes
drawnow;

Explanation

- Find Objects: `findobj` is used to locate the specific scatter plot objects for poles and zeros. The `Tag` property is used to identify these objects.

- Change Colors: Once the objects are found, their `MarkerEdgeColor` properties are modified to set different colors for poles and zeros.

- Refresh Plot: `drawnow` is called to ensure the plot updates with the new settings.

- AxesGrid: Accessing `AxesGrid` from the `pzplot` object helps in locating the scatter plots within the plot's internal structure.

- MATLAB Updates: As MATLAB updates its graphics system, the way objects are structured might change. Always check the latest documentation or use the `inspect` function in MATLAB to explore object properties interactively.

This approach should allow you to customize the colors of the poles and zeros separately in your `pzplot`. If you encounter any further issues, consider checking the MATLAB documentation or reaching out to MathWorks support for specific version-related changes.

[Jan]

Yeah, you just plugged my question into ChatGPT and pasted the answer of ChatGPT here. This is in no way helpful, only includes what I already did and doesn't work.

[Voss]

'I tried using the "findobj" method and ... I tried changing the color of the markers in those Scatter plots, but this does not seem to have an effect on the markers.'

That seems to work when run here (see below - all markers are of size 10 and linewidth 2, with the pole marker red and the zero marker blue).

s = tf('s');
f = 1 + 1/s;
pzp = pzplot(f);

pzp.Responses.MarkerSize = 10;
pzp.Responses.LineWidth = 2;

oPole = findobj(gca, 'Tag', 'PZPoleScatter');
oPole.MarkerEdgeColor = 'red';

oZero = findobj(gca, 'Tag', 'PZZeroScatter');
oZero.MarkerEdgeColor = 'blue';

[Jan]

Huh. Interesting. Okay, I just tried it again in my LiveScript, and it doesn't work in the LiveScript. But it does work in the regular Script! So, apprently something is different in the plot rendering in the live script!

Could you maybe test if the code also doesn't work for you in a LiveScript? That would be greatly appreciated!

[Voss]

"Could you maybe test if the code also doesn't work for you in a LiveScript?"

Unfortunately, my only option to run the code is here in the Answers forum because I don't have a license for any toolbox containing pzplot.

[Jan]

Ah, dang it. Well, that's a bummer. I hope anybody else can chime in here and could test it.

Answer 1

[Andrew Ouellette]

Hi Jan,

Starting in 24b, we introduced new chart and response objects for pzplot().

Each model you input to pzplot() will generate a single response object, which allows you to customize the styling for your response graphics. However, you are correct in that you can only pick a single styling for each response, which all graphics belonging to that response will then match. If you want to split the poles & zeros for a model, I recommend creating a pole-only model and a zero-only model.

s = tf('s');
f = (1 + 1/s);
fpoles = tf(1,f.Denominator{1});
fzeros = tf(f.Numerator{1},1);
pzp = pzplot(fpoles,fzeros);
pzp.Responses(1).MarkerSize = 10;
pzp.Responses(1).LineWidth = 2;
pzp.Responses(1).Color = 'r';
pzp.Responses(2).MarkerSize = 10;
pzp.Responses(2).LineWidth = 2;
pzp.Responses(2).Color = 'b';

●

Live scripts are a bit of an edge case when it comes to graphics. You'll find that the same behavior occurs when you save & load a figure containing a PZPlot- your changes made using findobj will be obliterated. Using findobj in this manner to change graphics within a PZPlot never notifies the chart object, and thus your changes cannot be serialized. Live scripts will only support changes made using our provided chart API.

[Jan]

Hello Andrew, thanks for chiming in!

I expected that I could somehow trigger a refresh of the plot using something like "refresh()" or "redraw()", but sadly that's not the case.

I guess I have to split my plot into poles and zeros as you suggested. At least that's a working solution!