# Cirle with color changing gradually.

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Hoang Phuc Ho on 17 Jul 2015
Commented: Aboozar Garavand on 19 Mar 2017
How can I plot a circle like this in matlab, please give me an example. Thanks in advance.

arich82 on 17 Jul 2015
Edited: arich82 on 17 Jul 2015
[Edited to add colorbar and image.]
As far as I know, you can't do it directly, but pol2cart is your friend. Look at
and maybe
% construct grid of polar coords
th = (0:5:360)*pi/180;
r = 0:.05:1;
[TH, R] = meshgrid(th, r);
% convert polar to cartesian
[X, Y] = pol2cart(TH, R);
% dummy function plotted over X Y data
Z = X + 1i*Y;
f = abs((Z.^4 - 1).^(1/4));
% use overhead view of surf plot for figure
figure;
surf(X, Y, f);
view(2);
axis equal;
axis square;
colorbar('SouthOutside');
colormap('Jet');
Note that axis(2) gives an overhead view, so it looks like a flat circle, and axis equal ensures it looks like a circle and not a distorted ellipse.
Walter Roberson on 18 Mar 2017
Unfortunately, surf() is not compatible with the new-ish polaraxes (R2016a and later).
You could use the older polar() to create the basic background graphic, and then "hold on", and then plot on top of it.

Walter Roberson on 18 Mar 2017
The File Exchange contribution https://www.mathworks.com/matlabcentral/fileexchange/17933-polar-to-from-rectangular-transform-of-images transforms rectangular images to and from polar to achieve the effect this Question is about.
Aboozar Garavand on 19 Mar 2017
Thank u, I solve the problem