[Octave-bug-tracker] [bug #39370] contourc adds duplicates to the start and end of the 1st level

[Rik]

Follow-up Comment #11, bug #39370 (project octave):

Just for fun, I put tic() and toc() around the uniquifying code and then did 


[xx,yy,zz] = sombrero ();
c = contourc (xx,yy,zz, 10);


Running this a few times the extra code adds 10-13 milliseconds to the run
time which isn't much.  I then increased the number of levels to 50 to stress
the code, but it still took only 25 milliseconds.

I don't think performance is the issue, but I do think finite precision is. 
For example,


[xx,yy,zz] = sombrero ();
c = contourc (xx,yy,zz, [0.95, 0.98, 0.99])
c =

 Columns 1 through 7:

    0.9500   -0.3618         0    0.3618    0.4000    0.5226    0.4000
   13.0000   -0.4000   -0.5226   -0.4000   -0.3618         0    0.3618

 Columns 8 through 14:

    0.3618         0   -0.3618   -0.4000   -0.5226   -0.4000   -0.3618
    0.4000    0.5226    0.4000    0.3618         0   -0.3618   -0.4000

 Columns 15 through 21:

    0.9800   -0.3024         0    0.3024         0   -0.3024    0.9900
    5.0000         0   -0.3024         0    0.3024         0    5.0000

 Columns 22 through 26:

   -0.1512         0    0.1512         0   -0.1512
         0   -0.1512         0    0.1512         0



For the contour at 0.95, the first and last entries are within an eps of each
other.


c(:,2) - c(:,14)
ans =

  -5.5511e-17
            0


Perhaps this speaks to working on this in the C++ code.



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