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Re: complex number
- From: Corinna Vinschen <corinna-cygwin at cygwin dot com>
- To: cygwin at cygwin dot com
- Date: Wed, 1 Apr 2009 19:30:54 +0200
- Subject: Re: complex number
- References: <8704.38224.qm@web25004.mail.ukl.yahoo.com>
- Reply-to: cygwin at cygwin dot com
On Apr 1 16:58, Marco Atzeri wrote:
> --- Mer 1/4/09, Corinna Vinschen ha scritto:
> > > I was trying to understand why this code
> > >
> > > #include <iostream>
> > > #include <complex>
> > >
> > > int main()
> > > {
> > >???double a = 0;
> > >???double b = 1. / a;
> > >???a += 1;
> > >???std::cout << std::abs
> > (std::complex<double> (b, a)) << '\n';
> > >? }
> > >
> > > produce Inf on most platform and NaN on cygwin.
> >
> > That's the result of the newlib function which is defined
> > as
> >
> > ? double
> > ? cabs(z)
> > ? struct complex z;
> > ? {
> > ? ? return hypot(z.x, z.y);
> > ? }
> >
>
> Hi Corinna,
> that is not correct as hypot( 0, Inf)
> return Inf and not NaN.
>
> There is a cabs backup implementation in libgcc that is probably
> the one used when system cabs is not available.
But cabs *is* exported by Cygwin and the function is the newlib
function. I can't tell you why you see what you see. I'm not
on good terms with this complex math thingy. That's why I think
you should really discuss this on the newlib list :}
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
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