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From "Phil Steitz (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-402) Complex.ZERO.pow(Complex.ONE) gives NaN in unit tests
Date Sun, 08 Aug 2010 14:58:15 GMT

    [ https://issues.apache.org/jira/browse/MATH-402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12896366#action_12896366
] 

Phil Steitz commented on MATH-402:
----------------------------------

The latest draft ISO C spec appears now to be public and is here:
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1494.pdf
The complex specifications are in Annex G.  Does not look like anything has changed since
C99x, though I have not done side-by-side comparisons.  It looks to me like what we have in
the code now matches the spec; but the spec does not specifically call out (unless I missed
it) specialization to real arguments.  What is causing the NaN is the singularity in the log
function.   Colt 1.1 looks like it matches our code.  R returns  0 + 0i.


> Complex.ZERO.pow(Complex.ONE) gives NaN in unit tests
> -----------------------------------------------------
>
>                 Key: MATH-402
>                 URL: https://issues.apache.org/jira/browse/MATH-402
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 2.2
>         Environment: Issue 15 http://code.google.com/p/symja/issues/detail?id=15
>            Reporter: Axel Kramer
>
> Why does this unit test in ComplexTest.java gives NaN?
> I expected to get Complex.ZERO as the result?
> {code:java} 
>    public void testPowZero() {
>        TestUtils.assertSame(Complex.NaN,
>                Complex.ZERO.pow(Complex.ONE));
> ...
>    }
> {code} 
> I would suggest something like this for the Complex#pow() method:
> {code:java} 
>     public Complex pow(Complex x) {
>         if (x == null) {
>             throw new NullPointerException();
>         }
>         if (x.imaginary == 0.0) {
>           if (real == 0.0 && imaginary == 0.0) {
>             if (x.real == 0.0){      	
>             	return Complex.ZERO;
>             }
>           }
>           if (x.real == 1.0) {
>           	return this;
>           }
>         }
>         return this.log().multiply(x).exp();
>     }
> {code} 
>  

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