Using drawnow and delete to move a circle on the last point of a line as it's x and y vectors grow

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Vasko Nechev 2017-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/340066-using-drawnow-and-delete-to-move-a-circle-on-the-last-point-of-a-line-as-it-s-x-and-y-vectors-grow

评论： Image Analyst 2017-5-13

I'm trying to learn something simple in Matlab. My ultimate goal is to create a simulation that models planets as they move around each other and are affected by each others orbits

What I want to do is track their path on a 2d plot with a solid line... but display their current position with a circle I tried to create a simple plot to test this

clear
clc
close all
x=[]
y=[]
n=0
z=0
m=0
run1=0
cirshow=[]
while m<2
  n=n+1
  m=m+.1
  x(n)=m
  y(n)=x(n)^2
    cirshow(n)=plot(x(n),y(n),'bo')
    plot(x,y,'b-')
    axis([0 3 0 3])
    hold on
    if run1==1
        delete(cirshow(n-1))
    end
    drawnow
    run1=1
end

so my idea with the code here is to hold on two plots... one for the line and one for each coordinate with a circle -and then delete the second to last circle each time with 'delete'

%% Any help on how to fix this... and maybe also how to improve its efficiency would be greatly appreciated.

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Answer 1

Vasko Nechev 2017-5-13

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https://ww2.mathworks.cn/matlabcentral/answers/340066-using-drawnow-and-delete-to-move-a-circle-on-the-last-point-of-a-line-as-it-s-x-and-y-vectors-grow#answer_266867

在 MATLAB Online 中打开

Never mind I fixed it! It was all due to a 'hold on' command in the wrong spot I think Learning coding is always like that

here is the fixed code

clear
clc
close all
x=[];
y=[];
n=0;
z=0;
m=0;
run1=0;
cirshow=[];
while m<2
  n=n+1;
  m=m+.1;
  x(n)=m;
  y(n)=x(n)^2;
    cirshow(n)=plot(x(n),y(n),'bo')
    hold on
    plot(x,y,'b-')
    axis([0 3 0 3]);
    if run1==1
        delete(cirshow(n-1))
    end
    drawnow
    run1=1;
end

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Answer 2

Image Analyst 2017-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/340066-using-drawnow-and-delete-to-move-a-circle-on-the-last-point-of-a-line-as-it-s-x-and-y-vectors-grow#answer_266864

You may want to throw in a pause(0.2) in right before the end of the loop. Change the number to control the speed.

Also, you can compute your x, y, and z all in advance of the loop. And use a for loop instead of a while loop.

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Vasko Nechev 2017-5-13

yea I could ! are for loops faster than while loops? do you know by any chance?

Image Analyst 2017-5-13

在 MATLAB Online 中打开

I would think any timing differences would be insignificant. But you can try it yourself

n = 1000000 % A million iterations
tic;
for k = 1 : n
end
toc
tic
k = 1;
while k <= n
  k = k + 1;
end
toc
Elapsed time is 0.001823 seconds.
Elapsed time is 0.002494 seconds.

With a million iterations the difference is only about 0.6 milliseconds or so - not enough to notice. How many iterations do you plan on having?

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Using drawnow and delete to move a circle on the last point of a line as it's x and y vectors grow

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Using drawnow and delete to move a circle on the last point of a line as it's x and y vectors grow

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