Why is my circle invisible?

I can not figure out why my circle is invisiable when I plot it (It is a regression). Am I missing something? It used to work earlier.

x = [5; 4; -1; 1];
y = [3; 5; 2; 1];

% circle's equation:  x^2+y^2 = 2xc1+2yc2+c3
a = [2.*x,2.*y,ones(length(x),1)];
b = [x.^2 + y.^2];
c = a\b;

x_m = c(1)/2;
y_m = c(2)/2;
r = sqrt(x_m^2 + y_m^2 -c(3));

% plot data points
plot(x,y,'o')
hold on
% plot center
plot(x_m,y_m,'+')
% plot circle
circle(x_m,y_m,r)
hold off

[KSSV]

For that we should have a look on the function circle.

[Jenny Andersen]

It is no function, only an expression.

Answer 1

[Walter Roberson]

viscircles([x_m, y_m], r)
axis equal

[Jenny Andersen]

Thanks, but it's still unvisiable as far as I can see.

[Walter Roberson]

x = [5; 4; -1; 1];
y = [3; 5; 2; 1];
% circle's equation:  x^2+y^2 = 2xc1+2yc2+c3
a = [2.*x,2.*y,ones(length(x),1)];
b = [x.^2 + y.^2];
c = a\b;
x_m = c(1)/2;
y_m = c(2)/2;
r = sqrt(x_m^2 + y_m^2 -c(3));
% plot data points
plot(x,y,'o')
hold on
% plot center
plot(x_m,y_m,'+')
% plot circle
viscircles([x_m,y_m],r)
hold off

produces

provided your graphics is working properly.

Note: if you happen to be using MacOS Catalina, then there have been some reports that only the first one or two lines drawn work and that additional graphics objects might not get drawn.

[Jenny Andersen]

Ok, that explains it. Thank you.

[Walter Roberson]

Which explains it? Do you happen to be using Catalina ?

[Jenny Andersen]

Not Catalina but Sierra. I have however been having technical problems with matlab ever since I got it, so I just figured it had something to do with this (perhaps).

The error I get is the following:

Error in untitled14 (line 16)
viscircles([x_m,y_m],r)

[Walter Roberson]

Which MATLAB release are you using, and do you have the Image Processing Toolbox (that defines viscircles())

[Walter Roberson]

There are File Exchange contributions to draw circles, including https://www.mathworks.com/matlabcentral/fileexchange/59244-circles