[Numpy-discussion] Error in tanh for large complex argument

[Mark Bakker]

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 <markbak at gmail.com> wrote:

> 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, and to check how other libraries do
> >this in case the above still misses something.
>
> >
> >	Pauli
>
>
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