[Rcpp-devel] Variable for loop

[Amina Shahzadi]

Hi Dear

My purpose is to make run of a variable for loop. Here I have assumed else
statement to be zero. Otherwise it could be anything for example in the
following code.
In this code, my main aim to run the slices loop according to rows.
does it now look ok?


Thank you

#include <RcppArmadillo.h>
using namespace Rcpp;
using namespace RcppArmadillo;
//[[Rcpp::depends(RcppArmadillo)]]
//[[Rcpp::export]]
arma::cube up(arma::mat a){
  int m = a.n_cols;
  int n = a.n_rows;
  int p = a.n_rows;
  arma::cube b(n, m, p);
  for(int i=0; i<n; i++){
      for(int j=0; j<m; j++){
        for(int q=0; q<i; q++){
         if(q==0){
           b(i, j, q) = a(i, j);
         }
         else{
           b(i, j, q) = b(i-1, j, q-1) * a(i, j);
         }
      }
    }
  }
  return b;
}

On Tue, Sep 27, 2016 at 2:51 PM, Avraham Adler <avraham.adler at gmail.com>
wrote:

> Hello.
>
> Once again, it is very unclear what you want to do. Can you please
> explain, in English not code what your procedure intends to do, the
> input you expect, and the output you expect?
>
> What it LOOKS like you want to do is to create an N x M x N cube where
> the first slice is your matrix and the remaining slices are all 0. If
> that is the case, There are much, much simpler ways to do it than to
> traverse all N²M cells. The following should work.
>
> #include <RcppArmadillo.h>
> using namespace Rcpp;
> using namespace RcppArmadillo;
> //[[Rcpp::depends(RcppArmadillo)]]
>
> //[[Rcpp::export]]
> arma::cube fillup(arma::mat a){
>   int m = a.n_cols;
>   int n = a.n_rows;
>   arma::cube C = arma::cube(n, m, n, arma::fill::zeros);
>
>   C.slice(0) = a;
>
>   return(C);
> }
>
> Avi
>
> On Mon, Sep 26, 2016 at 5:59 PM, Amina Shahzadi <aminashahzadi at gmail.com>
> wrote:
> > Hi Dear
> >
> > I have a problem in using a variable for loop in using RcppArmadillo
> > library.
> > I have pasting here my code. It is executing but not giving the same
> results
> > as its R code version gives. The results produced by it are really
> weird. I
> > have checked it step by step. It is because of the for (int q=0; q<i;
> q++).
> > I request tp please help how to handle it in cpp.
> >
> > The another question is I want to multiply the cube b(i, ,) by a scalar.
> How
> > can we consider the entire columns and slices of a cube for each of the
> > rows.  "b(span(i), span(), span())"  is not working for me.
> >
> > Thank you
> >
> > #include <RcppArmadillo.h>
> > using namespace Rcpp;
> > using namespace RcppArmadillo;
> > //[[Rcpp::depends(RcppArmadillo)]]
> > //[[Rcpp::export]]
> > arma::cube up(arma::mat a){
> >   int m = a.n_cols;
> >   int n = a.n_rows;
> >   int p = a.n_rows;
> >   arma::cube b(n, m, p);
> >   for(int i=0; i<n; i++){
> >       for(int j=0; j<m; j++){
> >         for(int q=0; q<i; q++){
> >          if(q==0){
> >            b(i, j, q) = a(i, j);
> >          }
> >          else{
> >            b(i, j, q) = 0.0;
> >          }
> >       }
> >     }
> >   }
> >   return b;
> > }
> >
> > --
> > Amina Shahzadi
>



-- 
*Amina Shahzadi*
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