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Sébastien Brisard edited comment on MATH613 at 7/27/11 7:51 AM:

Here is a patch for {{combine}} and {{combineToSelf}} (i.e. the linear, bivariate case). File
name is {{MATH61320110727.patch}}.
was (Author: celestin):
Here is a patch for {{combine}} and {{combineToSelf}} (i.e. the linear, bivariate case).
> Equivalent of Blas DAXPY
> 
>
> Key: MATH613
> URL: https://issues.apache.org/jira/browse/MATH613
> Project: Commons Math
> Issue Type: New Feature
> Affects Versions: 3.0
> Reporter: Sébastien Brisard
> Priority: Minor
> Labels: linear, vector
> Attachments: MATH61320110727.patch
>
>
> In Blas, the method {{DAXPY}} computes an inplace 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 CommonsMath. 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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