Signed infinity and signed zero Re: [Maxima] proposal to change acos

>>>>> "Richard" == Richard Fateman  writes:

    Richard> Basically, if you have a system that has signed
    Richard> infinities (as IEEE 754) you end up with signed zeros.

    Richard> For a probably too-long discussion of this, see extrat.pdf
    Richard> in www.cs.berkeley.edu/~fateman/papers/   also refs.

    Richard> Projective and affine mode rational numbers are also
    Richard> possible. This would give us in affine mode,
    Richard> one (unsigned + or -   infinity) which is 1/0.

    Richard> Why introduce this?  because a +b/c  should be
    Richard> computed as   a    if  c=1/0.   This allows one
    Richard> to continue to compute, even after a division by 0.

    Richard> If you have +inf and -inf you should also have +0 and -0,
    Richard> and 0/0= undef. (projective mode)

    Richard> This could/should be added to the Lisp, and then allowed
    Richard> to show through for Maxima.

Hmm.  This complicates things quite a bit because as far as I know,
only cmucl and sbcl support signed zeroes.  Thus, we can't just
convert log(-1.0 - 0.0 *%i) into (cl:log #c(-1.0 -0.0)).  We have to
do this ourselves.  Of course, we would have to do this ourselves for
bigfloats, so perhaps that's not so bad.

We will also have to prevent maxima from converting -0.0*%i to 0.
(Curiously, maxima cvs on cmucl says -0.0*%i is -0.0)

Ray