Re: Is infinity equal to infinity?

Joachim Durchholz <joachim.durchholz@munich.netsurf.de>
10 Jul 1998 21:01:53 -0400

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From: Joachim Durchholz <joachim.durchholz@munich.netsurf.de>
Newsgroups: sci.math.num-analysis,sci.math,comp.compilers
Date: 10 Jul 1998 21:01:53 -0400
Organization: Compilers Central
Distribution: inet
References: 98-07-058
Keywords: arithmetic

Erik Runeson wrote:
>
> When comparing floating-point numbers, should infinity (Inf) be
> concidered equal to infinity?
>
> Inf == Inf ?


This depends on what infinity you have.
For example, Intel x87 floating-point arithmetic has the following
infinities:
      1/0 positive infinity
    -1/0, log(0) negative infinity
These may compare equal to each other or not, depending on the mode the
chip is in: in "affine" mode, they are different, in "projective" mode,
they are considered equal.
(There is a range of numbers called "indefinite" that result from things
like 0/0, sqrt(-1), or log(-1). These are nevery considered equal to an
infinity; I don't know how they compare to each other. MS C++ has an
_isnan() function that checks for infinities and indetermates.)


HTH
Joachim
--

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