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Date: Wed, 27 Jul 2011 14:51:10 +0000 (UTC)
From: =?utf-8?Q?S=C3=A9bastien_Brisard_=28JIRA=29?= <jira@apache.org>
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Subject: [jira] [Updated] (MATH-613) Equivalent of Blas DAXPY
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     [ https://issues.apache.org/jira/browse/MATH-613?page=3Dcom.atlassian.=
jira.plugin.system.issuetabpanels:all-tabpanel ]

S=C3=A9bastien Brisard updated MATH-613:
-----------------------------------

    Attachment: MATH-613-20110727.patch

You're right. I've eliminated as much duplicate code as possible. This is i=
ndeed cleaner. Also checked the "Grant license to ASF" button...
Sorry for the mess.

> Equivalent of Blas DAXPY
> ------------------------
>
>                 Key: MATH-613
>                 URL: https://issues.apache.org/jira/browse/MATH-613
>             Project: Commons Math
>          Issue Type: New Feature
>    Affects Versions: 3.0
>            Reporter: S=C3=A9bastien Brisard
>            Priority: Minor
>              Labels: linear, vector
>         Attachments: MATH-613-20110727.patch, MATH-613-20110727.patch, MA=
TH-613-20110727.patch
>
>
> In Blas, the method {{DAXPY}} computes an in-place linear combination of =
two vectors. More precisely, a call to {{DAXPY(a, x, y)}} updates vector {{=
y}} with the value of {{a * x + y}}. This can lead to very compact code, wh=
ich I feel the need for in Commons-Math. However, DAXPY also has its limita=
tions. For example, it cannot perform the other combination {{y <- x + a * =
y}}.
> I think it would be useful that {{RealVector}} had a method for computing=
 {{a * this + b * y}}, and storing the result in {{this}}. In the spirit of=
 the {{mapToSelf}} method, I propose to create two new methods in {{Interfa=
ce RealVector}}
> {noformat}RealVector map(BivariateRealFunction f, RealVector y){noformat}
> and
> {noformat}RealVector mapToSelf(BivariateRealFunction f, RealVector y){nof=
ormat}
> The former would return a new vector {{v}} such that
> {noformat}v[i] <- f(this[i], y[i])}}{noformat}
> and the latter would update {{this}},
> {noformat}this[i] <- f(this[i], y[i]){noformat}
> Emulating {{DAXPY}} would then simply be a matter of implementing the app=
ropriate bivariate function.
> While we are at it, how about
> {noformat}RealVector map(TrivariateRealFunction f, RealVector y, RealVect=
or z){noformat}
> {noformat}RealVector mapToSelf(TrivariateRealFunction f, RealVector y, Re=
alVector z){noformat}

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