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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-971) FastMath.atanh wrong?
Date Fri, 03 May 2013 11:24:16 GMT

    [ https://issues.apache.org/jira/browse/MATH-971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13648335#comment-13648335
] 

Gilles commented on MATH-971:
-----------------------------

Here is what I obtain:

----+--------------------
 x  |  FastMath.atanh(x)
----+--------------------
0.0 | 0.0
0.1 | 0.10033534773107558
0.2 | 0.2027325540540821
0.3 | 0.3095196042031118
0.4 | 0.42364893019360184
0.5 | 0.5493061443340549
0.6 | 0.6931471805599454
0.7 | 0.8673005276940534
0.8 | 1.0986122886681098
0.9 | 1.4722194895832204
1.0 | Infinity
----+---------------------

Please post your code.

                
> FastMath.atanh wrong?
> ---------------------
>
>                 Key: MATH-971
>                 URL: https://issues.apache.org/jira/browse/MATH-971
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.1.1
>            Reporter: Luke Nezda
>
> When I compare the values computed using FastMath.atanh with those produced by similar
C++ code (using standard math.h), the results are different.  The C++ code agrees with WolframAlpha
(e.g., [http://www.wolframalpha.com/input/?i=atanh(1)]), so I think it is probably right.
> ||Input||Wolfram-Alpha||C++ / math.h||FastMath.atanh||
> |0.1 |0.10033534773107558|0.100335|0.09966865249116204|
> |0.2 |0.2027325540540822| 0.202733|0.19739555984988078|
> |0.3 |0.30951960420311175|0.30952 |0.2914567944778671|
> |0.4 |0.4236489301936|    0.423649|0.3805063771123649|
> |0.5 |0.5493061443340548| 0.549306|0.4636476090008061|
> |0.6 |0.6931471805599453| 0.693147|0.5404195002705842|
> |0.7 |0.8673005276940531| 0.867301|0.6107259643892086|
> |0.8 |1.0986122886681098| 1.09861 |0.6747409422235527|
> |0.9 |1.4722194895832204| 1.47222 |0.7328151017865066|
> |1	 |Infinity|           inf     |0.7853981633974483|
> |1.1 |1.522 and 1.571i|   -nan    |0.8329812666744317|

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