[Octave-bug-tracker] [bug #54896] voronoi produces no edges for provided data

[Rik]

Update of bug #54896 (project octave):

                Category:               Libraries => Octave Function        
                 Release:                   4.2.1 => dev                    

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Follow-up Comment #6:

As I understand it, Matlab still uses QHull.  It just doesn't expose the API
to programmers anymore.  With Matlab, you are stuck using whatever options
they think are appropriate.

But, I don't think this is a problem with the QHull library.  The voronoi
function in voronoi.m does post-processing on the edges found.  I think there
may be an issue there.  The code is


  if (numel (x) > 2)
    ## Eliminate the edges of the diagram representing the box.
    ## Exclude points outside a certain radius from the center of
distribution.
    ## FIXME: Factor should be at least 1.0.  Octave uses 1.1 for margin.
    ## There is no theoretical justification for this choice.
    ctr = [(xmax + xmin)/2 , (ymax + ymin)/2];
    radius = 1.1 * sumsq ([xmin, ymin] - ctr);
    dist = sumsq (p - ctr, 2);

    p_inside = (1:rows (p))(dist < radius);
    edge_inside = any (ismember (edges, p_inside));
    edges = edges(:, edge_inside);


If I change the factor from 1.1 to 100.1 then I get a figure equivalent to
Matlab.  If I comment out the code completely I get an en equivalent figure as
well. 


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