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

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MathWorks Support Team
on 26 Jul 2010

Commented: Walter Roberson
on 9 Sep 2022 at 16:33

I would like to plot a circle with a given radius and center.

### Accepted Answer

MathWorks Support Team
on 23 Mar 2022

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:

viscircles(centers,radii)

##### 18 Comments

Walter Roberson
on 9 Sep 2022 at 16:33

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.)

### More Answers (9)

Supoj Choachaicharoenkul
on 2 Oct 2019

plot(x, y, 'bo', 'MarkerSize', 50);

##### 2 Comments

Walter Roberson
on 5 Feb 2022

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

##### 3 Comments

amine bouabid
on 23 Jul 2018

Edited: amine bouabid
on 23 Jul 2018

hello

you can plot a circle simply by writing :

syms x; syms y;

ezplot((x-xi).^2+(y-yi).^2-r.^2)

where xi and yi are the coordinates of the center and r is the radius

##### 2 Comments

Walter Roberson
on 9 May 2021

Using viscircles() or using plot() with a 'o' marker and large 'MarkerSize' is even shorter.

Ebrahim Soujeri
on 26 Mar 2021

The shortest code for it could be this:

function plotcircle(r,x,y)

th = 0:pi/100:2*pi;

f = r * exp(j*th) + x+j*y;

plot(real(f), imag(f));

##### 3 Comments

Walter Roberson
on 27 Mar 2021

Notice though that I used the shortcut of plotting a single variable instead of real() and imag() of the expression. This is a "feature" of plot: if you ask to plot() a single variable and the variable is complex valued, then it uses the real component as x and the imaginary component as y. Removing the temporary variables made the code more compact, but the change to plot() only a single expression is using a different algorithm than what you used.

.. and you did say "the shortest", but my version of your approach is shorter ;-)

PATRICIA AGUILAR
on 4 May 2021

##### 1 Comment

Walter Roberson
on 4 May 2021

See https://www.mathworks.com/matlabcentral/answers/98665-how-do-i-plot-a-circle-with-a-given-radius-and-center#answer_108013 for code to plot a circle.

For 67 degrees, notice that in

xunit = r * cos(th) + x;

yunit = r * sin(th) + y;

you could use cosd() and sind() if your angle were in degrees.

Devin Marcheselli
on 17 Jan 2020

how do i plot a circle using the equation: (x-h).^2+(y-k).^2 = r.^2

##### 3 Comments

Mark Rzewnicki
on 17 Mar 2020

Sadly I just saw this now, sorry.

The easiest way to do this would have been to write the original code twice (renaming the variables the second time) and plot both circles using a "hold on" statement.

This makes the code look brutally ugly - you really should vectorize things and define functions when scaling up code like this - but it will get the job done in a pinch. The result would look something like this (5-minute edit of my original code):

% Circle equation: (x-h)^2 + (y-k)^2 = r^2

% Center: (h,k) Radius: r

h = 1;

k = 1;

r = 1;

h1 = 2;

k1 = 2;

r1 = 2;

%% In x-coordinates, the circle "starts" at h-r & "ends" at h+r

%% x_res = resolution spacing between points

xmin = h - r;

xmax = h + r;

x_res = 1e-3;

X = xmin:x_res:xmax;

xmin1 = h1 - r1;

xmax1 = h1 + r1;

X1 = xmin1:x_res:xmax1;

%% There are 2 y-coordinates on the circle for most x-coordinates.

%% We need to duplicate every x-coordinate so we can match each x with

%% its pair of y-values.

%% Method chosen: repeat the x-coordinates as the circle "wraps around"

%% e.g.: x = [0 0.1 0.2 ... end end ... 0.2 0.1 0]

N = length(X);

x = [X flip(X)];

N1 = length(X1);

x1 = [X1 flip(X1)];

%% ytemp1: vector of y-values as we sweep along the circle left-to-right

%% ytemp2: vector of y-values as we sweep along the circle right-to-left

%% Whether we take positive or negative values first is arbitrary

ytemp1 = zeros(1,N);

ytemp2 = zeros(1,N);

ytemp11 = zeros(1,N1);

ytemp22 = zeros(1,N1);

for i = 1:1:N

square = sqrt(r^2 - X(i)^2 + 2*X(i)*h - h^2);

ytemp1(i) = k - square;

ytemp2(N+1-i) = k + square;

end

for i = 1:1:N1

square1 = sqrt(r1^2-X1(i)^2 + 2*X1(i)*h1 - h1^2);

ytemp11(i) = k1 - square1;

ytemp22(i) = k1 + square1;

end

y = [ytemp1 ytemp2];

y1 = [ytemp11 ytemp22];

%% plot the (x,y) points

figure(1)

plot(x,y)

hold on

plot(x1,y1)

axis([-5 5 -5 5]);

ali yaman
on 14 Apr 2022

Edited: ali yaman
on 14 Apr 2022

I think there is no need to any of the above solutions, you can draw a circle by one of the following codes.

Let's say radius is 5

fimplicit(@(x,y) x^2+y^2-25)

ezplot('x^2+y^2-25',[-5,5])

% Note that the 25 in the codes comes from the square of 5. If you want

% draw a circle with 8 radius then write 64 instead of 25.

Sam Zebrado
on 12 Jun 2022

Edited: Sam Zebrado
on 12 Jun 2022

You can use a one-line function like this if you need to plot circles on unequal axis but do not what them to look like ellipses:

%% a function to plot using different radius

fc_circle_plot = @(xs,ys,rs,varargin)...

arrayfun(@(x,y,r)plot(x,y,'o','MarkerSize',r,varargin{:}),xs,ys,rs,'UniformOutput',false);

%% one demo

x = 1:5;

y = rand(1,5);

radius = randi([10,20],1,5);% random integer from 10 to 20, with a size of [1,5]

figure;

hold on;

fc_circle_plot(x,y,radius,...

'Color','b','LineWidth',2 ... any parameters supported by plot() could be placed here

);

hold off;

p.s. You can also replace function plot as other functions for other usages.

##### 1 Comment

Walter Roberson
on 12 Jun 2022

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