[Numpy-discussion] numpy.arccos(numpy.inf)????
Hi -- Sorry to be a pest with corner cases, but I found another one. In this case, if you try to take the arccos of numpy.inf in the context of a complex array, you get a bogus return (IMO). Like this: In [147]: R = numpy.array([1, numpy.inf]) In [148]: numpy.arccos(R) Warning: invalid value encountered in arccos Out[148]: array([ 0., NaN]) In [149]: C = numpy.array([1+1j, numpy.inf]) In [150]: numpy.arccos(C) Warning: invalid value encountered in arccos Out[150]: array([ 0.90455689-1.06127506j, NaN -Infj]) The arccos(numpy.inf) in the context of a real array is OK, but taking arcocs(numpy.inf) in the context of a complex array should return NaN + NaNj, IMO. Thoughts? Stuart Brorson Interactive Supercomputing, inc. 135 Beaver Street | Waltham | MA | 02452 | USA http://www.interactivesupercomputing.com/ ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] numpy.arccos(numpy.inf)????
On Fri, May 16, 2008 at 11:47 AM, Stuart Brorson <[EMAIL PROTECTED]> wrote:
> Hi --
>
> Sorry to be a pest with corner cases, but I found another one.
>
> In this case, if you try to take the arccos of numpy.inf in the
> context of a complex array, you get a bogus return (IMO). Like this:
>
> In [147]: R = numpy.array([1, numpy.inf])
>
> In [148]: numpy.arccos(R)
> Warning: invalid value encountered in arccos
> Out[148]: array([ 0., NaN])
>
> In [149]: C = numpy.array([1+1j, numpy.inf])
>
> In [150]: numpy.arccos(C)
> Warning: invalid value encountered in arccos
> Out[150]: array([ 0.90455689-1.06127506j, NaN -Infj])
>
> The arccos(numpy.inf) in the context of a real array is OK, but taking
> arcocs(numpy.inf) in the context of a complex array should return
> NaN + NaNj, IMO.
>
> Thoughts?
Hmm, this works fine on OS X. This may be a problem with one of the
lower-level math functions which we defer to the platform.
In [1]: from numpy import *
In [2]: arccos(nan+nan*1j)
Out[2]: (nan+nanj)
In [3]: arccos(nan+0j)
Out[3]: (nan+nanj)
In [4]: arccos(nan)
Out[4]: nan
In [5]: arccos([1.0+0j, nan])
Out[5]: array([ 0. -0.j, NaN NaNj])
The implementations of the complex versions are in umathmodule.c.src
(for the expanded versions, see umathmodule.c after building); they
are all prefixed with "nc_". E.g. the following are calling nc_acos()
for doubles. Here is the source:
static void
nc_acos(cdouble *x, cdouble *r)
{
nc_prod(x,x,r);
nc_diff(&nc_1, r, r);
nc_sqrt(r, r);
nc_prodi(r, r);
nc_sum(x, r, r);
nc_log(r, r);
nc_prodi(r, r);
nc_neg(r, r);
return;
/* return nc_neg(nc_prodi(nc_log(nc_sum(x,nc_prod(nc_i,
nc_sqrt(nc_diff(nc_1,nc_prod(x,x;
*/
}
I suspect the problem comes from the nc_log() which calls your
platform's atan2() for the imaginary part of the result.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
-- Umberto Eco
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Re: [Numpy-discussion] numpy.arccos(numpy.inf)????
On Fri, May 16, 2008 at 1:37 PM, Robert Kern <[EMAIL PROTECTED]> wrote: > On Fri, May 16, 2008 at 11:47 AM, Stuart Brorson <[EMAIL PROTECTED]> wrote: >> Hi -- >> >> Sorry to be a pest with corner cases, but I found another one. >> >> In this case, if you try to take the arccos of numpy.inf in the >> context of a complex array, you get a bogus return (IMO). Like this: >> >> In [147]: R = numpy.array([1, numpy.inf]) >> >> In [148]: numpy.arccos(R) >> Warning: invalid value encountered in arccos >> Out[148]: array([ 0., NaN]) >> >> In [149]: C = numpy.array([1+1j, numpy.inf]) >> >> In [150]: numpy.arccos(C) >> Warning: invalid value encountered in arccos >> Out[150]: array([ 0.90455689-1.06127506j, NaN -Infj]) >> >> The arccos(numpy.inf) in the context of a real array is OK, but taking >> arcocs(numpy.inf) in the context of a complex array should return >> NaN + NaNj, IMO. >> >> Thoughts? > > Hmm, this works fine on OS X. Sorry, I'm an idiot. I get the same results as you when I read the message correctly. In [2]: arccos(inf+0j) Out[2]: (nan+-infj) -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] numpy.arccos(numpy.inf)????
2008/5/16 Stuart Brorson <[EMAIL PROTECTED]>: > Hi -- > > Sorry to be a pest with corner cases, but I found another one. > > In this case, if you try to take the arccos of numpy.inf in the > context of a complex array, you get a bogus return (IMO). Like this: > > In [147]: R = numpy.array([1, numpy.inf]) > > In [148]: numpy.arccos(R) > Warning: invalid value encountered in arccos > Out[148]: array([ 0., NaN]) > > In [149]: C = numpy.array([1+1j, numpy.inf]) > > In [150]: numpy.arccos(C) > Warning: invalid value encountered in arccos > Out[150]: array([ 0.90455689-1.06127506j, NaN -Infj]) > > The arccos(numpy.inf) in the context of a real array is OK, but taking > arcocs(numpy.inf) in the context of a complex array should return > NaN + NaNj, IMO. > > Thoughts? Is this so bad? lim x->inf arccos(x) = -j inf Granted this is only when x approaches infinity along the positive real axis... Anne ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] numpy.arccos(numpy.inf)????
Stuart Brorson schrieb: > Hi -- > > Sorry to be a pest with corner cases, but I found another one. [...] Mark and I spent a *lot* of time in fixing those edge cases in Python 2.6 and 3.0. We used the C99 standard as template. I recommend that you look at our code. Christian ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
