[Numpy-discussion] numpy.arccos(numpy.inf)????

Robert Kern robert.kern@gmail....
Fri May 16 13:39:01 CDT 2008


On Fri, May 16, 2008 at 1:37 PM, Robert Kern <robert.kern@gmail.com> wrote:
> On Fri, May 16, 2008 at 11:47 AM, Stuart Brorson <sdb@cloud9.net> 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


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