# How do I plot a circle with a given radius and center?

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MathWorks Support Team on 26 Jul 2010
Answered: Shengchao Lin on 11 Aug 2023
I would like to plot a circle with a given radius and center.

MathWorks Support Team on 4 Sep 2024 at 0:00
Edited: MathWorks Support Team on 23 Mar 2022
Here is a MATLAB function that plots a circle with radius 'r' and locates the center at the coordinates 'x' and 'y':
function h = circle(x,y,r) hold on th = 0:pi/50:2*pi; xunit = r * cos(th) + x; yunit = r * sin(th) + y; h = plot(xunit, yunit); hold off
An alternative method is to use the 'rectangle' function:
function h = circle2(x,y,r) d = r*2; px = x-r; py = y-r; h = rectangle('Position',[px py d d],'Curvature',[1,1]); daspect([1,1,1])
If you are using version R2012a or later and have Image Processing Toolbox, then you can use the 'viscircles' function to draw circles:
Image Analyst on 9 Sep 2022
@Yuvin Wickramanayake no. It means that you put that code into a script, maybe it was called testcircle.m and preceding that code you had code to call the function like
h = circle(x, y, r);
At least that's one possibility. If so, you'd need to close your circle() function with the "end" keyword, which will allow a function to be defined and called from within a script.
function h = circle(x,y,r)
hold on
th = 0:pi/50:2*pi;
xunit = r * cos(th) + x;
yunit = r * sin(th) + y;
h = plot(xunit, yunit);
hold off
end
If you still have trouble, attach your whole m-file in a NEW question (not here).
Walter Roberson on 9 Sep 2022
You would get a different error message if you had a script with a function after and the function did not have a matching end statement.
That error could happen if you try to create a function inside a script in a MATLAB version before R2015b. It might perhaps also happen if you try to define a function at the command line (I seem to remember the wording as being slightly different for that case, but perhaps that is the wording in an older version than I am using.)

serwan Bamerni on 17 Feb 2016
Edited: MathWorks Support Team on 26 May 2023
There is now a function called viscircles():
Walter Roberson on 17 Oct 2016
This is part of the Image Processing Toolbox
Walter Roberson on 25 Dec 2020

Steven Lord on 25 Dec 2020
Another possibility is to approximate the circle using a polyshape with a large number of sides and plot that polyshape.
p = nsidedpoly(1000, 'Center', [2 3], 'Radius', 5);
plot(p, 'FaceColor', 'r')
axis equal
Walter Roberson on 9 Jun 2021
Walter Roberson on 9 Jun 2021
Remember that an equilateral triangle has a 60 degree range.

Shengchao Lin on 11 Aug 2023
Using function "fplot" would be my simplest way:
Unit circle:
fplot(@(t) sin(t), @(t) cos(t));
grid on
Circle with center "x", "y" and radius "r":
x = 3; y = 4; r = 5;
fplot(@(t) r*sin(t)+x, @(t) r*cos(t)+y);
grid on;

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