On Mon, Sep 29, 2008 at 5:16 PM, Robert Kern <[EMAIL PROTECTED]> wrote:
> On Mon, Sep 29, 2008 at 18:10, Charles R Harris > <[EMAIL PROTECTED]> wrote: > > > > On Mon, Sep 29, 2008 at 4:54 PM, Charles R Harris > > <[EMAIL PROTECTED]> wrote: > >> > >> On Mon, Sep 29, 2008 at 4:40 PM, Charles R Harris > >> <[EMAIL PROTECTED]> wrote: > >>> > >>> On Mon, Sep 29, 2008 at 4:28 PM, Robert Kern <[EMAIL PROTECTED]> > >>> wrote: > >>>> > >>>> On Mon, Sep 29, 2008 at 17:13, Charles R Harris > >>>> <[EMAIL PROTECTED]> wrote: > >>>> > > >>>> > On Mon, Sep 29, 2008 at 3:52 PM, Charles R Harris > >>>> > <[EMAIL PROTECTED]> wrote: > >>>> >> > >>>> >> Hi All, > >>>> >> > >>>> >> I've been cleaning up the ufunc loops and the sign function > currently > >>>> >> doesn't have a defined behavior for nans. This makes the results > >>>> >> depend on > >>>> >> the order/type of comparisons in the code, which looks fragile to > me. > >>>> >> So > >>>> >> what should it return? I vote for nan but am open for suggestions. > >>>> > > >>>> > And while we're at it, lets decide how to treat max/min when nans > are > >>>> > involved. Or should we just say the behavior is undefined. > >>>> > >>>> When feasible, I would like float(s)->float functions to return NaN > >>>> when given a NaN as an argument. At least as the main versions of the > >>>> function. Specific NaN-ignoring functions can also be introduced, but > >>>> as separate functions. I don't know what exactly to do about > >>>> float->int functions (e.g. argmin). I also don't know how these should > >>>> interact with the current seterr() state. > >>> > >>> So the proposition is, sign, max, min return nan when any of the > >>> arguments is nan. > >>> > >>> +1 > >> > >> I also propose that all logical operators involving nan return false, > >> i.e., ==, !=, <, <=, >, >=, and, or, xor, not. > >> > > > > Currently this is so except for !=. On my machine nan != nan is true. > Looks > > like it is being computed in C as !(nan == nan). Hmm, anyone know of a C > > standard on this? > > C99 Annex F: > > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf > > In particular: > > """ > F.8.3 Relational operators > x != x -> false The statement x != x is true if x is a NaN. > """ > Thanks, that was very helpful. I wonder how widespread the less, lessequal, etc. macros are? Chuck
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