From: numpy-discussion-boun...@scipy.org [numpy-discussion-boun...@scipy.org]
On Behalf Of Mark Bakker [mark...@gmail.com]
Sent: 28 January 2011 12:45
To: numpy-discussion@scipy.org
Subject: Re: [Numpy-discussion] Error in tanh for large complex argument
Good point, so we need a
Fri, 28 Jan 2011 12:57:18 +0100, Mark Bakker wrote:
> Follow up:
>
> The behavior is correct for real argument:
[clip]
> So maybe we should look there for good logic,
In the real case you can do "if (abs(z) > cutoff) return sgn(z)",
which is not the right thing to do for complex numbers.
Anyway,
Follow up:
The behavior is correct for real argument:
In [20]: sinh(1000)
Out[20]: inf
In [21]: cosh(1000)
Out[21]: inf
In [22]: tanh(1000)
Out[22]: 1.0
So maybe we should look there for good logic,
Mark
On Fri, Jan 28, 2011 at 11:45 AM, Mark Bakker wrote:
> Good point, so we need a better
Good point, so we need a better solution that fixes all cases
>> I'll file a ticket.
>>
>> Incidentally, if tanh(z) is simply programmed as
>>
>> (1.0 - exp(-2.0*z)) / (1.0 + exp(-2.0*z))
>This will overflow as z -> -\infty. The solution is probably to use a
>different expression for Re(z) < 0, a
Fri, 28 Jan 2011 11:25:19 +0100, Mark Bakker wrote:
> I'll file a ticket.
>
> Incidentally, if tanh(z) is simply programmed as
>
> (1.0 - exp(-2.0*z)) / (1.0 + exp(-2.0*z))
This will overflow as z -> -\infty. The solution is probably to use a
different expression for Re(z) < 0, and to check how
I'll file a ticket.
Incidentally, if tanh(z) is simply programmed as
(1.0 - exp(-2.0*z)) / (1.0 + exp(-2.0*z))
the problem is fixed.
Thanks, Mark
[clip]
> > Not for large complex values:
> >
> > In [85]: tanh(1000+0j)
> > Out[85]: (nan+nan*j)
>
> Yep, it's a bug. Care to file a ticket?
>
> The
On Thu, Jan 27, 2011 at 8:37 PM, Nadav Horesh wrote:
> The C code return the right result with glibc 2.12.2 (linux 64 + gcc 4.52).
Same for me on mac os x (not sure which C library it is using, the
freebsd one ?) for ppc, i386 and amd64,
cheers,
David
___
: 27 January 2011 13:11
To: numpy-discussion@scipy.org
Subject: Re: [Numpy-discussion] Error in tanh for large complex argument
Thu, 27 Jan 2011 11:40:00 +0100, Mark Bakker wrote:
[clip]
> Not for large complex values:
>
> In [85]: tanh(1000+0j)
> Out[85]: (nan+nan*j)
Yep, it's a
Thu, 27 Jan 2011 11:40:00 +0100, Mark Bakker wrote:
[clip]
> Not for large complex values:
>
> In [85]: tanh(1000+0j)
> Out[85]: (nan+nan*j)
Yep, it's a bug. Care to file a ticket?
The implementation is just sinh/cosh, which overflows.
The fix is to provide an asymptotic expansion (sgn Re z),
a
Hello list,
When computing tanh for large complex argument I get unexpected nans:
tanh works fine for large real values:
In [84]: tanh(1000)
Out[84]: 1.0
Not for large complex values:
In [85]: tanh(1000+0j)
Out[85]: (nan+nan*j)
While the correct answer is:
In [86]: (1.0-exp(-2.0*(1000+0j)))/
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