> On Nov 2, 2018, at 21:19 , Daniel Herring <dherr...@tentpost.com> wrote: > > Hi Marco, > > I would just rely on the IEEE 754 values and define constants for > convenience. Negative zero is an artifact of floating-point calculations, > not a symbol in math. Don't forget that many values are classified as NaN > (common exponent, many fractions).
Thanks. That is what I was thinking... > C defines fpclassify() and related predicates to return NaN, infinite, zero, > subnormal, or normal. Yes. Bu the point is that I would like to stay in CL-land as much as possible. > Obligatory reference: What Every Computer Scientist Should Know About > Floating-Point Arithmetic by David Goldberg > > Rounding error causes loss of life: > http://www-users.math.umn.edu/~arnold/disasters/patriot.html Exactly. Cheers — Marco > > > - Daniel > > > On Fri, 2 Nov 2018, Antoniotti Marco wrote: > >> Dear all >> I am fooling around (again!) with the spec of a math library that I want the >> students to work on as a project. Language is Common Lisp. >> Essentially the library is an extended generic math library built on the >> basis of the many ones floating around. >> Now. Here comes IEEE. And “infinity" >> Among many implementations there is more or less a consensus about how to >> “represent” IEEE infinities in CL. >> E.g. >> LW > math:long-float-positive-infinity >> +1D++0 #| +1D++0 is double-float plus-infinity |# >> CCL ? math:long-float-positive-infinity >> 1D++0 >> and so on. >> NaN is not as clearly defined. >> LW 45 > math:nan >> 1D+-0 #| 1D+-0 is double-float not-a-number |# >> CCL ? math:nan >> 1D+-0 #| not-a-number |# >> But to get a NaN in SBCL/CMUCL requires a trick. I use >> (sb-kernel:make-double-float -524288 0)) ; Courtesy of Raymond Toy. >> In any case… There are two issues that I would like to brainstorm a bit. >> The first one pertains rounding modes. Give the current state of affairs, >> it does not seem possible to access them in all the CL implementations. >> CMUCL/SBCL give you the necessary hooks, but LW doesn’t. >> Let’s skip this. >> The second is just a simple question. >> Given that we *do* have (with some acrobatics) access to IEEE infinities, >> would you add symbolic constants to such library like >> (defconstant +posinf+ ‘+posinf+) >> or would you just rely on the IEEE infinities? >> Generic functions like >> (defgeneric plus (x y) …) >> Will obviously be affected. >> I just want to get a feeling about the overall wisdom of this crowd. >> All the best >> Marco >> -- >> Marco Antoniotti -- Marco Antoniotti, Associate Professor tel. +39 - 02 64 48 79 01 DISCo, Università Milano Bicocca U14 2043 http://bimib.disco.unimib.it Viale Sarca 336 I-20126 Milan (MI) ITALY Please check: http://cdac2019.lakecomoschool.org Please check: http://troncopackage.org Please check: https://www.frontiersin.org/research-topics/7394/network-bioscience Please note that I am not checking my Spam-box anymore. Please do not forward this email without asking me first (cum grano salis).