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

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.

Answer 1

[Vasko Nechev]

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

Answer 2

[Image Analyst]

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.

[Vasko Nechev]

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

[Image Analyst]

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?