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. """ -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion