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Re: Negative zeros?


From: Przemek Klosowski
Subject: Re: Negative zeros?
Date: Wed, 14 Sep 2005 15:59:51 -0400 (EDT)

   I am sorry, John, David, and Stephan. I am a mathematician. I don't 
   choose to read nonsense. Zero is zero is zero.

   I realize that e-1000000 is positive and -e-1000000 is negative and 
   that these might be represented by 0 and -0 respectively on a 
   machine. But I will never accept that
       0 * (-1) = -0.

OK, so as a mathematician you should be well receptive to Kahan's
arguments, stemming from the complex analysis where there is a
definite need to distinguish lim(x>0, x->0) from lim(x<0, x->0)
because of branch cuts---otherwise, what would be the value of
sqrt(i*x-1) in each case?

Actually, Octave doesn't do it this way; sqrt(-1-0i)=sqrt(-1+0i)
but the concept of signed zeros does make sense if you understand
when it's appropriate.



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