[jira] [Commented] (MATH-613) Equivalent of Blas DAXPY

["Phil Steitz (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MATH-613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13063376#comment-13063376 ] 

Phil Steitz commented on MATH-613:
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I see the value of this based on the linear combination example, so am +0 to add the first two. It might be better, though to s/map/combine in the names.  It might also be good to explicitly name the linear combination example.  Are there other examples likely to be commonly used that anyone can think of?  If not, we should consider adding only the linear combination, since if that is all anyone will use, it will simplify the API to just name and add it.

Regarding the trivariate versions, what exactly are the use cases?

> 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: Sébastien Brisard
>            Priority: Minor
>              Labels: linear, vector
>
> 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, which I feel the need for in Commons-Math. However, DAXPY also has its limitations. 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 {{Interface RealVector}}
> {noformat}RealVector map(BivariateRealFunction f, RealVector y){noformat}
> and
> {noformat}RealVector mapToSelf(BivariateRealFunction f, RealVector y){noformat}
> 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 appropriate bivariate function.
> While we are at it, how about
> {noformat}RealVector map(TrivariateRealFunction f, RealVector y, RealVector z){noformat}
> {noformat}RealVector mapToSelf(TrivariateRealFunction f, RealVector y, RealVector z){noformat}

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