| Re: Inverse Hyberbolic Tangent [message #33346] |
Wed, 18 December 2002 10:29 |
Patrick L. Nolan
Messages: 1
Registered: December 2002
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Junior Member |
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p.pall <p.pall@atm.ox.ac.uk> wrote:
> Does anyone out there know how to compute INVERSE hypebolic tangent in IDL
> 5.5?
> An 'Atanh' function does not appear to exist.
> Does this mean I'll have to mess about with series expansions?
This one is easy to do on paper.
If y = atan(x),
then x = .5 * ln( (1+y) / (1-y) )
Of course you need to worry about singular behavior at
the boundaries and the possibility of invalid y values.
--
* Patrick L. Nolan *
* W. W. Hansen Experimental Physics Laboratory (HEPL) *
* Stanford University *
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| Re: Inverse Hyberbolic Tangent [message #33350 is a reply to message #33346] |
Wed, 18 December 2002 05:39  |
notspecified
Messages: 14
Registered: February 2002
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Junior Member |
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On Wed, 18 Dec 2002 13:26:18 -0000, "p.pall" <p.pall@atm.ox.ac.uk>
wrote:
> Hi,
>
> Does anyone out there know how to compute INVERSE hypebolic tangent in IDL
> 5.5?
>
> An 'Atanh' function does not appear to exist.
>
How about using complex numbers? According to Abramowitz and Stegun
4.6.16,
Arctanh( z ) = -i Arctan( i z )
Matt Feinstein does not include his email address
in the text of usenet postings.
--------
Harvard Law of Automotive Repair: Anything that goes away
by itself will come back by itself.
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