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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-620) multiplication of infinity
Date Fri, 02 Sep 2011 22:24:09 GMT
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[ https://issues.apache.org/jira/browse/MATH-620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13096432#comment-13096432
]

Gilles commented on MATH-620:
-----------------------------

These
{quote}
Assert.assertEquals(w.getReal(), neginf, 0);
Assert.assertEquals(w.getImaginary(), neginf, 0);
{quote}
behave as intended: all infinities are mapped to a single "point at infinity" (chosen to be
"INF" a.k.a. (+inf, +inf)), which IIRC is a way to deal with the infinite number of infinities
along all the directions in the complex plane.

This one
{quote}
Assert.assertEquals(w, z.divide(Complex.ONE.divide(z)));
{quote}
looks wrong indeed.

> multiplication of infinity
> --------------------------
>
>                 Key: MATH-620
>                 URL: https://issues.apache.org/jira/browse/MATH-620
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>            Reporter: Arne PlĂ¶se
>            Priority: Minor
>
> Take the following testcase
> {code}
> Assert.assertEquals(neginf, inf* neginf, Double.MIN_VALUE);  // <--Passes ordinary
double
> Assert.assertEquals(new Complex(neginf, 0), new Complex(inf, 0).multiply(new Complex(neginf,
0)));// <-- Fail only real parts no imaginary parts
> {code}
> The outcome of multiply is Complex.INF if one part is infinity.
> why not simply compute the multiplication and thats is?

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