[Octave-bug-tracker] [bug #56515] griddatan errors when querying with only one valid point

[Kai Torben Ohlhus]

Update of bug #56515 (project octave):

                Severity:              3 - Normal => 1 - Wish               
                Priority:              5 - Normal => 3 - Low                
              Item Group:        Unexpected Error => Feature Request        
                  Status:                    None => Patch Submitted        

    _______________________________________________________

Follow-up Comment #1:

Thank you for the bug report.  I noticed, that Matlab R2019a errors for your
example as well:


Error using builtin
QH6154 qhull precision error: initial facet 1 is coplanar with the interior
point
ERRONEOUS FACET:

While executing:  | qhull d Qt Qbb Qc
Options selected for Qhull 2010.1 2010/01/14:
  run-id 1522627653  delaunay  Qtriangulate  Qbbound-last  Qcoplanar-keep
  _pre-merge  _zero-centrum  Qinterior-keep  Pgood  _max-width  1
  Error-roundoff 1.4e-15  _one-merge 9.7e-15  Visible-distance 2.8e-15
  U-coplanar-distance 2.8e-15  Width-outside 5.5e-15  _wide-facet 1.7e-14

The input to qhull appears to be less than 3 dimensional, or a
computation has overflowed.

Qhull could not construct a clearly convex simplex from points:

The center point is coplanar with a facet, or a vertex is coplanar
with a neighboring facet.  The maximum round off error for
computing distances is 1.4e-15.  The center point, facets and distances
to the center point are as follows:


facet p1 p2 p0 distance=    0
facet p3 p2 p0 distance=    0
facet p3 p1 p0 distance=    0
facet p3 p1 p2 distance=    0

These points either have a maximum or minimum x-coordinate, or
they maximize the determinant for k coordinates.  Trial points
are first selected from points that maximize a coordinate.

The min and max coordinates for each dimension are:
  0:         0         1  difference=    1
  1:         0         1  difference=    1
  2:         0         1  difference=    1

If the input should be full dimensional, you have several options that
may determine an initial simplex:
  - use 'QJ'  to joggle the input and make it full dimensional
  - use 'QbB' to scale the points to the unit cube
  - use 'QR0' to randomly rotate the input for different maximum points
  - use 'Qs'  to search all points for the initial simplex
  - use 'En'  to specify a maximum roundoff error less than 1.4e-15.
  - trace execution with 'T3' to see the determinant for each point.

If the input is lower dimensional:
  - use 'QJ' to joggle the input and make it full dimensional
  - use 'Qbk:0Bk:0' to delete coordinate k from the input.  You should
    pick the coordinate with the least range.  The hull will have the
    correct topology.
  - determine the flat containing the points, rotate the points
    into a coordinate plane, and delete the other coordinates.
  - add one or more points to make the input full dimensional.


This is a Delaunay triangulation and the input is co-circular or
co-spherical:
  - use 'Qz' to add a point "at infinity" (i.e., above the paraboloid)
  - or use 'QJ' to joggle the input and avoid co-circular data


Error in qhullmx

Error in delaunayn (line 101)
t = qhullmx(x', 'd ', opt);

Error in griddatan>linear (line 105)
  tri = delaunayn(x);

Error in griddatan (line 89)
        yi = linear(x,y,xi,opt);


Thus this item should be treated as feature request.

But I can confirm, that the three line patch of bug #45542 fixes the original
problem.  We should concentrate on bug #45542 and fix this item as "side
effect".

    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?56515>

_______________________________________________
  Message sent via Savannah
  https://savannah.gnu.org/