From: Marius Vollmer <marius.vollmer@uni-dortmund.de>
Cc: guile-devel@gnu.org
Subject: Re: ratio implementation
Date: Tue, 14 Oct 2003 15:03:41 +0200 [thread overview]
Message-ID: <ljk778ynrm.fsf@troy.dt.e-technik.uni-dortmund.de> (raw)
In-Reply-To: <3F8A853D.1020708@ccrma> (Bill Schottstaedt's message of "Mon, 13 Oct 2003 03:58:05 -0700")
Bill Schottstaedt <bil@ccrma.Stanford.EDU> writes:
> I made the requested changes (using the Oct-9 CVS Guile):
>
> ftp://ccrma-ftp.stanford.edu/pub/Lisp/gratio-1.tar.gz
With your new files, I now get
guile> (inexact->exact 123456789123456789.0)
0
This might have to do with your clever continued fraction
approximation procedure.
Also:
guile> (define pi (* 2 (acos 0)))
guile> (- (inexact->exact pi) pi)
3.31628058347633e-10
Shouldn't we be able to do better than this? Double precision is good
to about 2e-16 and I would expect the fraction returned from
inexact->exact to be accurate within that margin. (I don't know
inexact->really why I expect this, it just seems to make sense.)
What about this approach: find the integer correspondig to the bits of
the mantissa of the double number (a bignum) and then correct for the
scaling and the exponent either by multiplying with a power of two, or
building a fraction with that power of two.
I don't have the details ready yet, but I think I'll try to come up
with code for this... (when it isn't already in GMP).
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next prev parent reply other threads:[~2003-10-14 13:03 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-07-28 11:24 ratio implementation Bill Schottstaedt
2003-07-28 12:08 ` Han-Wen Nienhuys
2003-07-29 0:41 ` Kevin Ryde
2003-07-29 11:57 ` Bill Schottstaedt
2003-07-30 22:42 ` Kevin Ryde
2003-09-15 10:35 ` Marius Vollmer
2003-09-15 16:19 ` Rob Browning
2003-09-15 22:06 ` Dirk Herrmann
2003-09-15 22:59 ` Kevin Ryde
2003-09-16 11:39 ` Bill Schottstaedt
2003-09-16 21:36 ` Rob Browning
2003-09-18 21:09 ` Dirk Herrmann
2003-10-07 15:26 ` Marius Vollmer
2003-10-13 10:58 ` Bill Schottstaedt
2003-10-14 8:57 ` Marius Vollmer
2004-02-18 14:25 ` fractions.test Bill Schottstaedt
2003-10-14 12:39 ` ratio implementation Marius Vollmer
2003-10-14 22:56 ` Kevin Ryde
2003-10-14 13:03 ` Marius Vollmer [this message]
2003-10-14 23:37 ` Kevin Ryde
2003-10-16 11:49 ` Bill Schottstaedt
2003-10-17 10:09 ` Marius Vollmer
2003-10-17 11:47 ` Bill Schottstaedt
2003-10-17 15:04 ` Rob Browning
2003-10-18 0:45 ` Kevin Ryde
2003-10-15 12:57 ` Bill Schottstaedt
2003-10-17 10:20 ` Marius Vollmer
2003-10-17 15:14 ` Rob Browning
2003-10-17 15:42 ` Marius Vollmer
2003-10-14 23:01 ` Kevin Ryde
2003-10-18 0:55 ` ash using shifts (was: ratio implementation) Kevin Ryde
2003-10-07 15:24 ` ratio implementation Marius Vollmer
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