[Numpy-discussion] Apropos ticked #913

David Cournapeau david@ar.media.kyoto-u.ac...
Wed Mar 4 23:53:55 CST 2009


Robert Kern wrote:
> On Wed, Mar 4, 2009 at 23:32, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
>
>   
>> One thing that still bothers me a bit is the return value of fmax/fmin when
>> comparing two complex nan values. A complex number is a nan whenever the
>> real or imaginary part is nan, and currently the functions return such a
>> number but originally they returned a complex number with both parts set to
>> nan. The current implemetation was a compromise that kept the code simple
>> while never explicitly using a nan value, i.e., the nan came from one of the
>> inputs. I avoided the explicit use of a nan value because the NAN macro was
>> possibly unreliable at the time. I'm open to thoughts on what the behavior
>> should be.
>>     
>
> Do we have examples from other implementations?
>   

For R, I believe there is no Nan complex number: 1+NaN * 1i, NaN, NaN+1i
are all printed the same as NaN, and according to the doc on complex
number (?Im):

     Complex vectors can be created with 'complex'.  The vector can be
     specified either by giving its length, its real and imaginary
     parts, or modulus and argument.  (Giving just the length generates
     a vector of complex zeroes.)

     'as.complex' attempts to coerce its argument to be of complex
     type: like 'as.vector' it strips attributes including names. All
     forms of 'NA' and 'NaN' are coerced to a complex 'NA', for which
     both the real and imaginary parts are 'NA'.

I would guess this is a consequence of R biased toward statistics, with
Na being mostly for missing data ?

cheers,

David




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