[Numpy-discussion] Apropos ticked #913

[Charles R Harris]

On Wed, Mar 4, 2009 at 1:57 PM, Pauli Virtanen <pav at iki.fi> wrote:

> Wed, 04 Mar 2009 13:18:55 -0700, Charles R Harris wrote:
> [clip]
> > There are python max/min and their behaviour depends on the scalar type.
> > I haven't looked at the numpy scalars to see precisely what they do.
> >
> > Numpy max/min are aliases for amax/amin defined when the core is
> > imported. The functions amax/amin in turn map to the array methods
> > max/min which call the maximum.reduce/minimum.reduce ufuncs, so they all
> > propagate nans, i.e., if the array contains a nan, nan will be the
> > return value.
> >
> > The nonpropagating comparisons are the ufuncs fmax/fmin and there are no
> > corresponding array methods. I think fmax/fmin should be renamed
> > fmaximum/fminimum before the release of 1.3 and the names fmax/fmin
> > reserved for the reduced versions to match the names amax/amin. I'll do
> > that if there are no objections.
>
> Aren't the nonpropagating versions of `amax` and `amin` called `nanmax`
> and `nanmin`? But these are functions, not array methods.
>
> What does the `f` in the beginning of `fmax` and `fmin` stand for?
>

The functions fmax/fmin are C standard library names, I assume the f stands
for floating like the f in fabs. Nanmax and nanmin work by replacing nans
with a fill value and then performing the specified operation. For instance,
nanmin replaces nans with inf. In contrast, the functions fmax and fmin are
real ufuncs and return nan when *both* the inputs are nans, return the
non-nan value when only one of the inputs is a nan, and do the normal
comparisons when both inputs are valid.

Chuck
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