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From "Jake Mannix (JIRA)" <j...@apache.org>
Subject [jira] Created: (MATH-313) Functions could be more object-oriented without losing any power.
Date Thu, 29 Oct 2009 08:08:59 GMT
Functions could be more object-oriented without losing any power.
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                 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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