[Rcpp-devel] Returning a matrix from RcppEigen

Hi Michael,

Thanks for reporting -- things like this signal that we could do better
error reporting, e.g. it might be more appropriate to see

Error in eval(expr, envir, enclos) (from srcConn#6) :
        Wrong R type for mapped vector (expected 'double', got 'integer')

or something to that effect. You might consider logging an issue at
https://github.com/RcppCore/RcppEigen so that we might tackle it later.

Cheers,
Kevin


On Fri, Jun 27, 2014 at 11:31 AM, Michael Hannon
<jmhannon.ucdavis at gmail.com> wrote:

Thanks, Dirk.  Last night I woke up with a cramp in my leg and the
inspiration that the problem was in the R test code, not in the call
to Eigen.  I was absent-mindedly creating integer matrices in my test
code.  After I changed to:

    amat <- matrix(as.numeric(1:9), nrow=3)

etc., the Eigen stuff worked just fine.  Sorry for the noise.

-- Mike

On Fri, Jun 27, 2014 at 2:38 AM, Dirk Eddelbuettel <edd at debian.org> wrote:

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