how to let a "plot" immune on any later " hold off" once this "plot" is created.

I am a Matlab fan.

pls review my Matlab script file below:

clear;clc;
r=10;
plot([-35,35], [0,0], 'r-.' )
axis equal
hold on
for h=linspace(0,10,10)
    theta=linspace(0,2*pi);
    x=r*cos(theta);
    y=30+h+r*sin(theta);
    plot(x,y);
    xlim([-50,50]);
    ylim([-50,50]);
    pause(0.1)
    
end

if I don't add " hold off" in the " for-end" statement, then the circle creates many ones when it is moving.

if I do add " hold off" in the " for-end" statement, then the horizontal red line is disappeared.

I expect :

1) the horizontal red line is kept once it is ploted before the the " for-end" statement.

2) only one circle is occuring when it is moving.

may you give me a guide?

Thanks in advance!

Answer 1

[DGM]

Here's one idea.

r=10;
plot([-35,35], [0,0], 'r-.' )
axis equal
hold on

% just create a dummy plot object to be used in the loop
hp = plot(0,0);
for h=linspace(0,10,10)
    theta=linspace(0,2*pi);
    x=r*cos(theta);
    y=30+h+r*sin(theta);
    
    % update the plot object with xy data
    hp.XData = x;
    hp.YData = y;
   
    xlim([-50,50]);
    ylim([-50,50]);
    pause(0.1)
end

There are other ways. I'd try to pull more stuff outside the loop.

% these don't need to be inside the loop
r = 10;
h = linspace(0,10,10);
theta = linspace(0,2*pi);

plot([-35,35], [0,0], 'r-.' )
axis equal
hold on

% these probably don't need to be inside the loop either
xlim([-50,50]);
ylim([-50,50]);

for k = 1:numel(h)
    x = r*cos(theta);
    y = 30 + h(k) + r*sin(theta);
    
    if k == 1 
        % create a new plot object on the first iteration
        hp = plot(x,y);
    else
        % update the plot object with xy data on subsequent passes
        hp.XData = x;
        hp.YData = y;
    end
    
    pause(0.1)
end

[Shawtone]

thank you!

[Shawtone]

H1=plot(0,0,'b');

H2=plot(0,0,'b');

H3=plot(0,0,'b');

...

H99=plot(0,0,'b');

H100=plot(0,0,'b');

do you know how to creat a plot loop?

thank you in advance！

[DGM]

I'm not sure what you're asking for.

If you want to create a bunch of handles to graphics objects, use an array, and not numbered variables like that. You can use gobjects() to preallocate an array which can be populated with handles inside a loop of some sort.

In the given example, there are only ever two line objects: the dashed line and the circle. The second object simply gets its properties updated, so there isn't a new handle to store.

It's possible you intend to capture the axes/figure as a raster image and store those -- for example, to output as an animated GIF or something. For example:

https://www.mathworks.com/matlabcentral/answers/1650520-error-creating-an-animated-gif-in-matlab

https://www.mathworks.com/matlabcentral/answers/1968669-i-need-help-animating-the-evolution-of-a-polar-plot-and-saving-it-as-a-gif

[Shawtone]

I close this issue under your guide.

thank you.