Thread Subject:

Function to plot circle !!!!

I wish to write a function [x, y] = getCircle (center,r) to get the x and y
coordinates of a circle.
The circle will be centered at center (2-element vector containing the x and y values of the center) and will have radius r.
x and y, have to be returned such that plot(x, y) will plot the circle.

I have used the polar equation for the circle.

function [x,y] = getCircle(center, r)
for i=0 : 0.001 : 2*pi;
    x = r*cos(i) + center(1);
    y = r*sin(i) + center(2);
end

I do not know how to call this function......so that output values [x,y] can be used to plot the circle on the command window.
If I wish to use the Cartesian equation....
(x-a)^2 - (y-b)^2 = r^2, how am I supposed to write the function ?

Please help !!!!!

On Jan 20, 3:10 pm, "Animesh Pandey" <apanimesh...@gmail.com> wrote:
[snip]
> Please help !!!!!
-------------------------------------------------------------------------

Did you see the FAQ!!!!!
http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F

Sir, I read the FAQ but that wasn't what what I needed.
I am basically having a problem in calling the function I mentioned before.
I am not able to use the output values [x,y] to plot the circle from the command window.

"Animesh Pandey" wrote in message <ihba3c$1fh$1@fred.mathworks.com>...
> Sir, I read the FAQ but that wasn't what what I needed.
> I am basically having a problem in calling the function I mentioned before.
> I am not able to use the output values [x,y] to plot the circle from the command window.

function [x,y] = getCircle(center, r)
%quick and dirty fix
for i=1:1000
    x(i) = r*cos(i) + center(1);
    y(i) = r*sin(i) + center(2);
end

function [x,y] = getCircle(center, r)
%better results than before, find out why
for i=1:1000
    x(i) = r*cos(i/100) + center(1);
    y(i) = r*sin(i/100) + center(2);
end

"Paulo Silva" wrote in message <ihbbi8$5qg$1@fred.mathworks.com>...
> function [x,y] = getCircle(center, r)
> %better results than before, find out why
> for i=1:1000
> x(i) = r*cos(i/100) + center(1);
> y(i) = r*sin(i/100) + center(2);
> end

r=10; % radius
center=[20,30]; % center cordinates
t=-pi:0.001:pi;
x=r*cos(t)+center(1);
y=r*sin(t)+center(2);

plot(x,y), axis square

Yumnam Kirani Singh
Trongalobi Awang Leikai

"Paulo Silva" wrote in message <ihbbi8$5qg$1@fred.mathworks.com>...
> function [x,y] = getCircle(center, r)
> %better results than before, find out why
> for i=1:1000
> x(i) = r*cos(i/100) + center(1);
> y(i) = r*sin(i/100) + center(2);
> end

This gave a better plot....thanks !!!!
I want to know how should I call this function so that it plots the circle
'cause if I write

hold on
grid on
plot(x , y ,'--r'), axis square

it plots only one point !!!!!
Can you help me with this !!!!

"Yumnam Kirani" <kirani.singh@gmail.com> wrote in message <ihbgna$4po$1@fred.mathworks.com>...
>
> plot(x,y), axis square
>
This command gave the 'circular' plot.....thankyou....
I was getting an elliptical plot before !!!! :D

"Animesh Pandey" <apanimesh061@gmail.com> wrote in message
news:ihba3c$1fh$1@fred.mathworks.com...
> Sir, I read the FAQ but that wasn't what what I needed. I am basically
> having a problem in calling the function I mentioned before.
> I am not able to use the output values [x,y] to plot the circle from the
> command window.

theta = 0:0.01:2*pi;
r = 5;
x = r*cos(theta);
y = r*sin(theta);
plot(x, y)
axis square

--
Steve Lord
slord@mathworks.com
To contact Technical Support use the Contact Us link on
http://www.mathworks.com

On Jan 21, 9:31 am, "Steven_Lord" <sl...@mathworks.com> wrote:

> theta = 0:0.01:2*pi;
> r = 5;
> x = r*cos(theta);
> y = r*sin(theta);
> plot(x, y)
> axis square
>
-------------------------------------------------------------
On Jan 21, 7:44 am, "Animesh Pandey" <apanimesh...@gmail.com> wrote:
> > plot(x,y), axis square
>
> This command gave the 'circular' plot.....thankyou....
> I was getting an elliptical plot before !!!! :D
--------------------------------------------------------------------------------------

Note: "axis square" does not guarantee a circle on your monitor. For
example I just ran that on my widescreen notebook and it definitely
looks elliptical. It also depends on the video adapter settings.
With different adapter settings, it could look square.

On Jan 22, 5:39 am, ImageAnalyst <imageanal...@mailinator.com> wrote:
> On Jan 21, 9:31 am, "Steven_Lord" <sl...@mathworks.com> wrote:
>
> > theta = 0:0.01:2*pi;
> > r = 5;
> > x = r*cos(theta);
> > y = r*sin(theta);
> > plot(x, y)
> > axis square
>
> -------------------------------------------------------------
> On Jan 21, 7:44 am, "Animesh Pandey" <apanimesh...@gmail.com> wrote:> > plot(x,y), axis square
>
> > This command gave the 'circular' plot.....thankyou....
> > I was getting an elliptical plot before !!!! :D
>
> --------------------------------------------------------------------------------------
>
> Note: "axis square" does not guarantee a circle on your monitor.  For
> example I just ran that on my widescreen notebook and it definitely
> looks elliptical.  It also depends on the video adapter settings.
> With different adapter settings, it could look square.

Yes, I always use:
set(gca,...
    'DataAspectRatio',[1 1 1])