As 4.225 is inexact, it may be somewhat smaller that #e4.225 or somewhat greater than #e4.225. Therefore, whether rounding an inexact number very close to the edge of the rounding point goes up or down, seems irrelevant to me. BTW, explicit rounding normally is the last operation in an inexact calculation. Implicit rounding as in a basic operation (+, -, *, /) with inexact numbers does occur, of course, and here rounding even up and odd down (or reversely, I don't recall) may be usefull such as to have implicit roundings cancel each other as much as possible, though I imagine their are examples of calculations where this strategy accumulates inaccuracy rather than reducing it.
Just some thoughts, Jos -----Original Message----- From: users-boun...@racket-lang.org [mailto:users-boun...@racket-lang.org] On Behalf Of Pierpaolo Bernardi Sent: viernes, 30 de noviembre de 2012 10:02 To: Neil Toronto Cc: users@racket-lang.org Subject: Re: [racket] Decimal rounding problem On Thu, Nov 29, 2012 at 7:42 PM, Neil Toronto <neil.toro...@gmail.com> wrote: > On 11/29/2012 10:53 AM, Greg Graham wrote: >> Now, the unanswered question is why do Crystal Reports and Excel round >> 4.225 to 4.23? I don't think I'll find as helpful of a forum to answer that >> question as I have found for Racket. Thanks again for being such a great >> community! > > Aw, you buttered us up so nicely that I have to respond. They're probably > rounding twice: once to get a decimal number close to the original, and then > to the specified number of digits. Looks like that's it. This paper by William Kahan contains a nice example of the problems of excel rounding: http://www.cs.berkeley.edu/~wkahan/Mindless.pdf (the paper is long, the excel example is on page 3) P. ____________________ Racket Users list: http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
