[Rcpp-devel] RcppArmadillo and sugar

[Romain Francois]

This now works with Row and Col too, as in :

test.armadillo.sugar.ctor <- function(){

	fx <- cxxfunction( signature(x= "numeric") , '
	NumericVector xx(x) ;
	arma::mat m = xx + xx ;
	arma::colvec co = xx ;
	arma::rowvec ro = xx ;
     return List::create(
     	_["mat"] = m + m,
     	_["rowvec"] = ro,
     	_["colvec"] = co
     );
     ', plugin = "RcppArmadillo" )
	checkEquals( fx(1:10),
		list(
			mat = matrix( 4*(1:10), nrow = 10 ),
			rowvec = matrix( 1:10, nrow = 1 ),
			colvec = matrix( 1:10, ncol = 1 )
			)
		,
		msg = "Mat( sugar expression )" )
	
}

(But I still need to figure out about complex)

Romain

Le 18/08/10 21:59, Romain Francois a écrit :
> After some discussion this morning with Conrad (who develops Armadillo),
> we've come up with a way that is not too intrusive on armadillo itself
> (it adds about 6 lines of code), yet opens a door for RcppArmadillo to
> adds its own constructors to the Mat template class.
>
> I've added this one now :
>
> template <int RTYPE, bool NA, typename VECTOR>
> inline Mat( const Rcpp::VectorBase<RTYPE,NA,VECTOR>& X ) ;
>
> Those of you who are familiar with how sugar is implemented (e.g. who
> have read the sugar vignette) will recognize the VectorBase class which
> is the magic template that makes all of sugar possible. Anyway, with
> this (rev. 2039), one can directly write code that makes an arma::mat
> directly out of a sugar expression.
>
> Here is how it is tested in RcppArmadillo unit tests
>
>
> test.armadillo.sugar.ctor <- function(){
>
> fx <- cxxfunction( signature(x= "numeric") , '
> NumericVector xx(x) ;
> arma::mat m = xx + xx ;
> return wrap( m + m ) ;
>
> ', plugin = "RcppArmadillo" )
> checkEquals( fx(1:10),
> matrix( 4*(1:10), nrow = 10 ) ,
> msg = "Mat( sugar expression )" )
>
> }
>
> I need to take care of the special case of complex vectors though. Will
> do. But the key here is these two lines :
>
>
> NumericVector xx(x) ; // create a NumericVector from a SEXP
> arma::mat m = xx + xx ; // create a arma::mat from a sugar expression
>
> Romain
>
> Le 17/08/10 12:26, Romain Francois a écrit :
>> Hello,
>>
>> After the last thread, I looked again at armadillo and came up with a
>> way to make it aware of Rcpp sugar, so that we can create an armadillo
>> matrix from an Rcpp sugar expression, without having to assign the
>> expression into an Rcpp vector.
>>
>> For example :
>>
>> NumericVector xx(x) ;
>> arma::mat m = forward( xx + xx ) ;
>>
>> But also for complex expressions : (expressions that make complex
>> vectors ) :
>>
>> ComplexVector xx(x) ;
>> arma::cx_mat m = forward( exp( xx ) ) ;
>>
>>
>> It needs the svn version of both Rcpp and RcppArmadillo to work.
>> It does not deal with dimensions at the moment, it just makes a arma
>> matrix with one column, I'll deal with that later.
>>
>>
>> The name forward might not be the right verb here, I was also thinking
>> about "melt" so that we melt sugar into caramel, but I'd like to hear
>> what others do with sugar.
>>
>>
>>
>>
>> BTW, one thing this gives is the construct :
>>
>> arma::mat m = forward( NumericVector(x) ) ;
>>
>> which I believe will be more efficient than
>>
>> arma::mat m = Rcpp::as< arma::mat >( x ) ;
>>
>> because it makes less copies. However I have not yet found a way to make
>> it "borrow" the memory as in the advanced constructor in armadillo.
>>
>>
>> Romain


-- 
Romain Francois
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http://romainfrancois.blog.free.fr
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