Drew a circle for a specific point in my plot

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

[jonas]

If you have the image processing toolbox, then for circles you could use

viscircles([Xcenter Ycenter],R)

instead of the annotation.

[Tiago Dias]

I don't but i resolved by problem by doing just

plot(nPC_imp,mincumpress,'O','Color','red','MarkerSize',25);

It drews a circle O on the specific point i want.

[jonas]

That's a practical workaround! :)

[Tiago Dias]

viscircles for me does a vertical elipse, not a circle. the "Yraidus is way bigger than the xradius"

[Tiago Dias]

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

[jonas]

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.

Answer 1

[KSSV]

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

[Tiago Dias]

With your solution I have this, so the first plot the limits are modified, and I dont like that, if I disable axis equal I got what vircircle does. I prefer my plot with O but thanks for your time

[KSSV]

YOu can go for markers with circle i.e O and specify its size.

[Tiago Dias]

yes, thats what I said to jonas on the previous answer