On Wed, Jul 23, 2025 at 11:56:00AM +0000, Jörg Sommrey wrote:
> Hello Luis,
>
> the results look fine when the expected types in the two failing tests are
> adjusted. Don't know if it would break any "real" code, maybe "is_pdl" is
> just too strict here.
I believe there are good reasons for the qualifier float+ in the case
of, for example, a vector of bytes: on one hand, the euclidean
magnitude of a vector of integers is not necessarily integer: (3,4)->5
but (1,1)->1.4142... On the other hand, the magnitude of a large
vector of bytes may overflow a byte. Nevertheless, I expect the
magnitude of a complex to be real, not a complex. A complex with a
zero imaginary part works but wastes some time and space. Thus, it would be
ideal if one could specify both, float+ and real as qualifiers of the
output of magnover, but that doesn't work. Is there an alternative for
a more flexible way to determine the correct type of an output
parameter based on that of the inputs? Meanwhile, I can simply
take the real part of the magnitudes :)
Regards,
Luis
>
> t/ufunc.t:
> is_pdl $empty->magnover, sbyte('BAD'), "bad flag gets set on empty magnover";
> is_pdl +(sequence(4)+i())->magnover, double(4.242640), 'magnover correct for
> complex';
>
> Best regards,
> -jo
>
>
> On Wed 23 Jul 2025 04:52:24 AM CEST, Luis Mochan <moc...@icf.unam.mx> wrote:
>
> > Hello,
> >
> > In some of my programs I used the code such as
> >
> > $abs=$cvec->abs2->sumover->sqrt;
> >
> > to get the magnitude of a vector $cvec. I just replaced it to the cleaner
> >
> > $abs=$cvec->magnover;
> >
> > But then my program failed when I made the comparison
> >
> > if($abs > 0){...}
> >
> > with the message
> >
> > Can't compare complex numbers at lib/PDL/PP.pm line 1445.
> >
> > It is true that we shouldn't compare complex numbers, except for
> > equality, but, shouldn't the magnitude of a complex vector be a real
> > number instead of a complex number (with zero imaginary part)?
> >
> > I tried to fix it by replacing the qualifier 'float+' in the pp_def of
> > magnover in Ufunc.pd by the qualifier 'real', but then the tests fail
> > as bytes are not converted to floats.
> >
> > Best regards,
> >
> > Luis
>
>
>
--
o
W. Luis Mochán, | tel:(52)(777)329-1734 /<(*)
Instituto de Ciencias Físicas, UNAM | fax:(52)(777)317-5388 `>/ /\
Av. Universidad s/n CP 62210 | (*)/\/ \
Cuernavaca, Morelos, México | moc...@fis.unam.mx /\_/\__/
GPG: 791EB9EB, C949 3F81 6D9B 1191 9A16 C2DF 5F0A C52B 791E B9EB
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