Matlab Convhull Error. Not enough unique data point

Question

I have been receiving this error in Matlab when I tried to calculate the convex hull of a set of numbers inscribed by a circle. Here is the code, and the error I kept getting is: Error computing the convex hull. Not enough unique points specified.

for u = 1:50; 
  for v = 1:50;       
    if sqrt(((u-25)^2)+((v-25)^2)) <= 25
      c = convhull(u,v);
      plot(u(c),v(c),'r-',u,v,'b*')         
    end
  end
end

Points inscribed or on a circle:

Answer 1

In your code you are sending individual points to convhull. Instead determine all the points in the set first, then send them all to the function at once. Here's an example.

% create mesh
[u,v] = meshgrid(1:50,1:50);
% get indicies of points within the circle
idx = sqrt((u-25).^2+(v-25).^2) <= 25;
% filter outside points
u = u(idx);
v = v(idx);
% compute convex hull
c = convhull(u,v);
plot(u(c),v(c),'r-',u,v,'b.');

Results

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Side note: Formally a singleton set is convex thus it's its own convex hull. I'm not sure why MathWorks decided to return an error in this case.