[Octave-bug-tracker] [bug #57964] polyfit() results for polynomial degree greater or equal than number of data

[Rik]

Update of bug #57964 (project octave):

              Item Group:        Incorrect Result => Missed Error or Warning
                  Status:                    None => Confirmed              
                 Release:                   5.2.0 => dev                    

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Follow-up Comment #3:

Changing the item group to "Missed Error or Warning".  Bumping the Release to
"dev".  Marking as confirmed.

At the very least, it would be good to issue a warning.  The return value for
the degrees of freedom output "df" is -1 which is nonsensical.

I tested a bit with Matlab and it does return consistent outputs for the
second and third outputs S and MU.


[P, S, MU] = polyfit (...)


However, the values are definitely not unique.  If I call polyfit with a
single output I get


[p] = polyfit ([1 2],[3 4],2)
p = [0.3333  0   2.6667]


But when I call it with three outputs I get


[p, s, mu] = polyfit ([1 2],[3 4],2)
p = [0   0.7071  3.5]


Given this pseudo-randomness, I'm not sure we have to exactly match Matlab
behavior so much as issue a warning and be consistent.



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