Drew a circle for a specific point in my plot

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Tiago Dias 2018-7-10

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评论： Tiago Dias 2018-7-10

PRESS.mat

在 MATLAB Online 中打开

Hi,

My objective is how to draw a circle for the min(PRESS). I wrote the following code for an ellipse, but I had to adjust the Xcenter and Ycenter handly, but I would rather do this in a automatically form, because if i change the min(PRESS) for example for the first two entries, the values changes and the elipse dont circle the point i want.

load('PRESS')
[mincumpress,nPC_imp] = min(PRESS(2:end,:))
x_aux = [0:maxpcs]';
figure
plot(x_aux,PRESS,'-b','LineWidth',2);
hold on
plot(x_aux,PRESS,'.r','MarkerSize',15);
yl = ylim; ylim([yl(1) yl(2)]); 
xcenter = nPC_imp / xl(2) + 0.035
ycenter = mincumpress * (yl(2) - yl(1)) - 0.08
dim = [xcenter ycenter .05 .05];
annotation('ellipse',dim,'Color','red')
hold on
xlabel('PC Number'); ylabel('PRESS');title('PCA-CV (ckf)');

Thanks for your time

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Tiago Dias 2018-7-10

If You use viscircles, it does what I showed on the picture? a vertical elipse? or it really does an circle?

jonas 2018-7-10

编辑：jonas 2018-7-10

Yea that's correct. Any method where the radius is connected to the axes will give that result, unless the xticks and yticks are equal. Your solution is very practical as the center is connected to the axes while the radius is 'disconnected' from the axes.

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回答（1 个）

KSSV 2018-7-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/409612-drew-a-circle-for-a-specific-point-in-my-plot#answer_328212

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Let C be the point, where you want to draw a circle.

N = 10 ;
x = 1:N ;
y = rand(N,1) ;
[val,idx] = max(y) ;
C = [x(idx) y(idx)] ;
plot(x,y) ;
hold on
R = 0.1 ;   % Radius of circle 
th = linspace(0,2*pi) ;
xc = C(1)+R*cos(th) ;
yc = C(2)+R*sin(th) ;
plot(xc,yc,'r') ;
axis equal