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Re: unary mapper system redesigned + a few questions


From: John W. Eaton
Subject: Re: unary mapper system redesigned + a few questions
Date: Tue, 17 Nov 2009 15:04:41 -0500

On 17-Nov-2009, Jaroslav Hajek wrote:

| > If you preserve the -0 for real values, then I think you should also
| > preserve them for imaginary values.
| >
| >
| This is the "why?" I think you still haven't answered. If we do the
| auto-narrowing, why do we do it only for positive zeros? Dropping both would
| actually be more symmetric than the current behavior.

Try this:

  x = logspace (300, 309, 10)'
  y = complex (0, -1) ./ x
  z = log (y)

What happens?  What should happen?  I see a jump in the last value
when I think the result should be continuous.  Shouldn't the imaginary
part always be -pi/2?

I think the result I'm seeing is a bug in the Complex log function.
It should be using the information provided by the negative zero
imaginary part.

If you throw away the negative zero imaginary part before it even gets
to the log function, then there is no way to fix this problem.

jwe


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