# [Rcpp-devel] float for BigMatrix

Yue Li gorillayue at gmail.com
Tue Jun 2 04:58:21 CEST 2015

```Dear List,

I wonder if there is a way to convert a big matrix to ‘float’ instead of ‘double’ within a Rcpp program. The reason for using float is mainly for performance improvement.

For instance, I have a simple function named ‘print_bigmat’ as shown below.

As shown in the output, ‘double_bigmat' will save the correct values of the original matrix ‘x’ but not ‘float_bigmat’.

// [[Rcpp::export]]
int print_bigmat(SEXP pBigMat) {

XPtr<BigMatrix> xpMat(pBigMat);

const mat& double_bigmat = arma::Mat<double>((double *)xpMat->matrix(), xpMat->nrow(), xpMat->ncol(), false);

const fmat& float_bigmat = arma::Mat<float>((float *)xpMat->matrix(), xpMat->nrow(), xpMat->ncol(), false);

Rcout << double_bigmat << endl;

Rcout << float_bigmat << endl;

return 0;
}

Output:

> x <- matrix(rnorm(10), nrow=2)
> x
[,1]        [,2]      [,3]       [,4]       [,5]
[1,] -0.05514382 -0.03943825 1.4145593 -0.1161918  2.3282466
[2,] -1.22023371 -0.35592125 0.7714512  0.6865120 -0.3504811
-0.0551  -0.0394   1.4146  -0.1162   2.3282
-1.2202  -0.3559   0.7715   0.6865  -0.3505

-3.3865e-14  -8.6552e+04   4.5441e-07  -5.0912e+23  -1.5184e+34
-1.3456e+00  -1.9025e+00  -1.2828e+00  -1.6780e+00   1.9268e+00

[1] 0
>

Thanks much,
Yue

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