Re: [Gcl-devel] tan compilation problem

[Vadim V. Zhytnikov]

Camm Maguire пишет:
> Greetings!
>
> "Vadim V. Zhytnikov" <address@hidden> writes:
>
>
> > Camm Maguire пишет:
> >
> > > Hi Vadim, and thanks for the report!  A fix is always easier than a
> > > good report!!
> >
> > Thanks for quick fix! Now it works fine. Actually this new tan
> > definition improved some other related things.  For example
> > previosly (tan 1) gave some weird number and now it produces
> > something sensible and exactly the same as (tan 1.0) which
> > we certainly expect. I only still wonder why the old tan defined
> > via sin/cos doesn't work properly.
>
>
> Hmm.  If you can reproduce and report the errant behavior with an old
> build, I'll verify that it has been eliminated, and not still present
> somewhere in the functions called by number_tan.  Only if you feel
> there is still some possibility of bug here.  Right now, I get the
> same answer with (/ (sin 1) (cos 1)).

Maybe I confused you then just don't worry.
Now everything seems to be fine.

> > As for small nonzero values I'm not numerical calculus expert
> > but they seems to be OK.  First of all how can we expect to get
> > exact zero (cos (/ pi 2)) if (/ pi 2) is not exactly pi/2 (and
> > newer will be)?  So it seems that any value will do unless error
> > is too big.
>
>
> Once (/ pi 2) is represented as a float, you are of course right.  But
> if gcl had some type analogous to the rational type with which to
> represent this number and those similar, then stuff like (equal (/ 1
> (sqrt 2)) (cos (/ pi 4))) would return t, etc.  I'm sure maxima has
> some facility for this -- I don't know if it really belongs in a lisp
> system, though.

There is no symbolic pi in Common Lisp.  This pi is just _numerical_
constant.  Unlike Lisp Maxima has symbolic pi and know some exact rules
about it but Maxima's pi has nothing to do with Lisp's constant pi.

> So the question is if the following code is useless:
>
> object
> number_tan(object x)
> {
>         object r, c;
>         vs_mark;
>
>         c = number_cos(x);
>         vs_push(c);
>         if (number_zerop(c) == TRUE)
>                 FEerror("Cannot compute the tangent of ~S.", 1, x);
>         r = number_tan1(x);
>         vs_reset;
>         return(r);
> }

--
     Vadim V. Zhytnikov

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