[Rcpp-devel] Returning a matrix from RcppEigen

[Dirk Eddelbuettel]

On 26 June 2014 at 16:01, Michael Hannon wrote:
| Greetings.  I've been trying to get familiar with RcppArmadillo and RcppEigen.
| As my "Hello, world!" example I'm using matrix multiplication.  I got the
| Armadillo version to work, but I'm having trouble with the Eigen version.
| 
| I'm trying to mimic one of Dirk's gallery snippets:
| 
|     http://gallery.rcpp.org/articles/eigen-eigenvalues/
| 
| I've appended the details.  My problem is that I evidently don't know what to
| return from the function.  I've tried various alternatives, but the only one
| that compiles is:
| 
|     return C;  // C = A * B
| 
| This compiles but produces the error message:
| 
|     > mat_mul_eigen(amat, bmat)
|     Error in eval(expr, envir, enclos) (from srcConn#6) :
|         Wrong R type for mapped vector
| 
| I must be overlooking something obvious.  Suggestions welcome.  Thanks.

I am out at a conference and can't look in detail but I would invite you to
check the other examples in the package itself: The unit tests are one
source, the examples and FastLm are another and then there are the other
packages using RcppEigen as well as other Rcpp Gallery posts.  This should be
fixable pretty easily. 

Dirk

 
| -- Mike
| 
| (File is: mat_mul_eigen.cpp.  Executed in R via:
|     sourceCpp("./mat_mul_eigen.cpp")
| )
| 
| 
| #include <RcppEigen.h>
| 
| // [[Rcpp::depends(RcppEigen)]]
| 
| using Eigen::Map;               // 'maps' rather than copies
| using Eigen::MatrixXd;                  // variable size matrix,
| double precision
| using Eigen::VectorXd;                  // variable size vector,
| double precision
| 
| // [[Rcpp::export]]
| 
| MatrixXd  mat_mul_eigen(Map<MatrixXd> A_,
| Map<MatrixXd> B_) {
| 
|   MatrixXd C(A_ * B_);
| 
|   return C;
| }
| 
| 
| /*** R
| 
| library(microbenchmark)
| amat <- matrix(1:9, nrow=3)
| bmat <- matrix(10:18, nrow=3)
| 
| mat_mul_eigen(amat, bmat)
| 
| amat %*% bmat
| 
| microbenchmark(
|   amat %*% bmat,
|   mat_mul_eigen(amat, bmat)
| )
| 
| */
| _______________________________________________
| Rcpp-devel mailing list
| Rcpp-devel at lists.r-forge.r-project.org
| https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel

-- 
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org