Rcpp problem

eigencholAtA.cpp

// [[Rcpp::depends(RcppEigen)]]

#include <RcppEigen.h>
using namespace Rcpp;
using namespace Eigen;

MatrixXd AtA(const MatrixXd A) {
    int n = A.cols();

    return MatrixXd(n,n).setZero().selfadjointView<Lower>()
        .rankUpdate(A.adjoint());
}


// [[Rcpp::export]]
List cholAtA(const MatrixXd A)
{

    LLT<MatrixXd> llt = AtA(A);

    return List::create(Named("L") = MatrixXd(llt.matrixL()),
                        Named("R") = MatrixXd(llt.matrixU()));
}

/*** R
A <- matrix(1:6, ncol=2)
storage.mode(A) <- "double"
fp <- cholAtA(A)
fp$L - t(chol(t(A) %*% A))
fp$R - chol(t(A) %*% A)
*/

errors.txt

!> sourceCpp("eigen_cholAtA.cpp")
 eigen_cholAtA.cpp:19:19: error: no viable conversion from 'MatrixXd' (aka 'Matrix<double, Dynamic, Dynamic>') to 'LLT<MatrixXd>' (aka 'LLT<Matrix<double, Dynamic, Dynamic> >')
     LLT<MatrixXd> llt = AtA(A);
                   ^     ~~~~~~
 /Users/kbroman/Rlibs/RcppEigen/include/Eigen/src/Cholesky/LLT.h:52:49: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'MatrixXd' \
 (aka 'Matrix<double, Dynamic, Dynamic>') to 'const Eigen::LLT<Eigen::Matrix<double, -1, -1, 0, -1, -1>, 1> &' for 1st argument
 template<typename _MatrixType, int _UpLo> class LLT
                                                 ^
 1 error generated.
 make: *** [eigen_cholAtA.o] Error 1
 ccache clang++ -I/Library/Frameworks/R.framework/Resources/include -DNDEBUG   -I"/Users/kbroman/Rlibs/Rcpp/include" -I"/Users/kbroman/Rlibs/RcppEigen/include" -I"/Users/kbroman/Co\
 de/RcppEx" -I/usr/local/include   -fPIC  -g -O2 -Wall -Wno-sign-conversion -Wno-unused -fcolor-diagnostics -pedantic -mtune=native -Qunused-arguments -stdlib=libc++ -Wsign-compare\
  -c eigen_cholAtA.cpp -o eigen_cholAtA.o
 Error in sourceCpp("eigen_cholAtA.cpp") :
   Error 1 occurred building shared library.

test_eigencholAtA.R

library(Rcpp)
library(RcppEigen)
sourceCpp("eigencholAtA.cpp")