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From "Luc Maisonobe (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (MATH-181) Specify the maximum of digits when parsing a Fraction
Date Thu, 31 Jan 2008 22:41:08 GMT

    [ https://issues.apache.org/jira/browse/MATH-181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12564531#action_12564531
] 

luc edited comment on MATH-181 at 1/31/08 2:39 PM:
-------------------------------------------------------------

I have checked the ideas I had about denominator. They do not address your issue, so the patch
as applied is good.

However, I noticed the last statement in the private constructor was a call to reduce. This
seems strange to me because a known property of the recursive algorithm to build the convergents
cn=pn/qn is that they are already reduced. This is a result of applying the Bezout theorem
to the easily proved recursive property p(n)q(n-1) - p(n-1)q(n) = (-1)^(n+1). This property
holds even if a1 is completely wrong due to numerical errors.

When I remove this statement, the existing test succeed as expected. I did not find any related
information in the log message nor in JIRA.

May I remove this statement or did I miss something ?

      was (Author: luc):
    I have checked the ideas I had about denominator. They are do not address your issue,
so the patch as applied is good.

However, I noticed the last statement in the private constructor was a call to reduce. This
seems strange to me because a known property of the recursive algorithm to build the convergents
cn=pn/qn is that they are already reduced. This is a result of applying the Bezout theorem
to the easily proved recursive property p(n)q(n-1) - p(n-1)q(n) = (-1)^(n+1). This property
holds even if a1 is completely wrong due to numerical errors.

When I remove this statement, the existing test succeed as expected. I did not find any related
information in the log message nor in JIRA.

May I remove this statement or did I miss something ?
  
> Specify the maximum of digits when parsing a Fraction
> -----------------------------------------------------
>
>                 Key: MATH-181
>                 URL: https://issues.apache.org/jira/browse/MATH-181
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 1.1
>            Reporter: Niall Pemberton
>            Priority: Minor
>         Attachments: MATH-181-FractionDigitsLimit-v2.patch, MATH-181-FractionDigitsLimit.patch,
MATH-181-FractionMaxDenominator.patch
>
>
> Firstly, thanks for the Fraction code - I've adapated it for something I'm working on
and I didn't have a clue how to convert a decimal to a fraction :)
> Excel spreadsheets have the facility to specify a fraction format where you specify the
maximum number of denominator digits to display.
> So for example:
>     format "?/?" displays decimal values formatted in the range 1/2 to n/9
>     format "??/??" displays decimal values formatted in the range 1/2 to n/99
>     format "???/???" displays decimal values formatted in the range 1/2 to n/999 etc
> In excel then the value 0.6152 displays as 3/5, 8/13 and 510/829 respectively for the
above 3 formats.
> I'm attaching a patch for the Fraction class which adds a new constructor where the maximum
number of digits can be specified, rather than the epsilon value.

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