Sorry for the late reply. The cset by @rik went to the default branch, what will eventually become Octave 7. A quick test shows no precision warning will be thrown in Octave 7:

```
>> delaunayn([1 1; 2 2; 3 3; 4 4; 5 5])
error: __delaunayn__: qhull failed
error: called from
delaunayn at line 76 column 11
```

Octave 6.3.0:

```
>> delaunayn([1 1; 2 2; 3 3; 4 4; 5 5])
QH6239 Qhull precision error: Initial simplex is cocircular or cospherical. Use option 'Qz' for the Delaunay triangulation or Voronoi diagram of cocircular/cospherical points. Option 'Qz' adds a point "at infinity". Use option 'Qs' to search all points for the initial simplex.
While executing: | qhull d Qt Qbb Qc
Options selected for Qhull 2015.2 2016/01/18:
run-id 133097998 delaunay Qtriangulate Qbbound-last Qcoplanar-keep
_pre-merge _zero-centrum Qinterior-keep Pgood _max-width 4
Error-roundoff 6.9e-15 _one-merge 4.9e-14 Visible-distance 1.4e-14
U-coplanar-distance 1.4e-14 Width-outside 2.8e-14 _wide-facet 8.3e-14
QH6154 Qhull precision error: Initial simplex is flat (facet 1 is coplanar with the interior point)
While executing: | qhull d Qt Qbb Qc Qz
Options selected for Qhull 2015.2 2016/01/18:
run-id 133097998 delaunay Qtriangulate Qbbound-last Qcoplanar-keep
Qz-infinity-point _pre-merge _zero-centrum Qinterior-keep Pgood
_max-width 4 Error-roundoff 6.9e-15 _one-merge 4.9e-14
Visible-distance 1.4e-14 U-coplanar-distance 1.4e-14 Width-outside 2.8e-14
_wide-facet 8.3e-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:
- p1(v3): 2 2 0.45
- p5(v2): 3 3 4
- p4(v1): 5 5 3.6
- p0(v0): 1 1 0
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 6.9e-15. The center point, facets and distances
to the center point are as follows:
center point 2.75 2.75 2.019
facet p5 p4 p0 distance= 0
facet p1 p4 p0 distance= 0
facet p1 p5 p0 distance= 0
facet p1 p5 p4 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: 1 5 difference= 4
1: 1 5 difference= 4
2: 0 4 difference= 4
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 6.9e-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.
error: __delaunayn__: qhull failed
error: called from
delaunayn at line 76 column 11
```