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From "Luc Maisonobe (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-313) Functions could be more object-oriented without losing any power.
Date Sat, 31 Oct 2009 16:14:59 GMT

    [ https://issues.apache.org/jira/browse/MATH-313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12772259#action_12772259
] 

Luc Maisonobe commented on MATH-313:
------------------------------------

This consensus is fine to me.
If you want to provide a patch, I'll be glad to apply it. What about ComposableFunction or
CompositableFunction for the name (I don't know which one is real english) ? It could be an
interface with an abstract class underneath or simply an abstract class. I agree that not
many people would want to provide their own implementation for composition.


> Functions could be more object-oriented without losing any power.
> -----------------------------------------------------------------
>
>                 Key: MATH-313
>                 URL: https://issues.apache.org/jira/browse/MATH-313
>             Project: Commons Math
>          Issue Type: New Feature
>    Affects Versions: 2.0
>         Environment: all
>            Reporter: Jake Mannix
>             Fix For: 2.1
>
>
> UnivariateRealFunction, for example, is a map from R to R.  The set of such functions
has tons and tons of structure: in addition to being an algebra, equipped with +,-,*, and
scaling by constants, it maps the same space into itself, so it is composable, both pre and
post.
> I'd propose we add:
> {code}
>   UnivariateRealFunction plus(UnivariateRealFunction other);
>   UnivariateRealFunction minus(UnivariateRealFunction other);
>   UnivariateRealFunction times(UnivariateRealFunction other);
>   UnivariateRealFunction times(double scale);
>   UnivariateRealFunction preCompose(UnivariateRealFunction other);
>   UnivariateRealFunction postCompose(UnivariateRealFunction other);
> {code}
> to the interface, and then implement them in an AbstractUnivariateRealFunction base class.
 No implementer would need to notice, other than switching to extend this class rather than
implement UnivariateRealFunction.
> Many people don't need or use this, but... it makes for some powerfully easy code:
> {code}UnivariateRealFunction gaussian = Exp.preCompose(Negate.preCompose(Pow2));{code}
> which is even nicer when done anonymously passing into a map/collect method (a la MATH-312).

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