Hi Jos,
I have nothing sensible to say about line 340 and
the fix you propose (probably it is right), but the
initial problem with 0.0 originates not in line 340
but rather in lines 330-331
(if (zero? N-abs)
(values 0 0 (if exactly? significand-precision 0))
or line 311
[exponent (- significand-precision e-adjust)
When we do (~r 0.0 #:notation 'exponential #:precision 4),
significand-precision is equal to 4 and e-adjust happens
to be zero.
Regards,
Dmitry
On 05/08/2013 11:21 AM, Jos Koot wrote:
I came across another thing:
#lang racket
(define x #e100.e-50000)
(rational? x) ; #t
(log x) ; -inf.0
(exact->inexact x); 0.0
(~r x #:notation 'exponential) ; error inexact->exact: no exact
representation
number: -inf.0
I think this is introduced in line 340 of racket/format.rkt which contains:
(inexact->exact (floor (/ (log N-abs) (log base))))
for the first estimate of the order of magnitude.
As the docs of ~r say "The exactness or inexactness of x does not affect its
formatting.", this behaviour may well be intentional.
It is possible though to avoid the error by subtracting the log of the
denominator from that of the nominator after conversion to exact rational.
Proc order-of-magnitude (in math I think) does this, but is for base 10
only. May be I should adapt order-of-magnitude such as to accept a base
argument?
Best wishes, Jos
-----Original Message-----
From: users-boun...@racket-lang.org
[mailto:users-boun...@racket-lang.org] On Behalf Of Dmitry Pavlov
Sent: martes, 07 de mayo de 2013 19:12
To: users@racket-lang.org
Subject: [racket] ~r: formatting 0.0 with 'exponential and #:precision
Hello,
I just came across the following oddness with formatting
of real numbers:
> (~r 1.0 #:notation 'exponential #:precision '(= 4))
"1.0000e+00"
OK
> (~r 0.0 #:notation 'exponential #:precision '(= 4))
"0.e+04"
???
Is there a rational explanation of why did
the requested precision go into the exponent
number for 0.0?
Thanks.
Best regards,
Dmitry
____________________
Racket Users list:
http://lists.racket-lang.org/users
____________________
Racket Users list:
http://lists.racket-lang.org/users
