The following example fails to compile: #include "Eigen/Core" #include "unsupported/Eigen/AutoDiff" int main (int argc, char const *argv[]) { typedef Eigen::AutoDiffScalar<Eigen::Vector3d> AD; const double _cv1_3 = 1.0; const AD chi_3 = 1.0; // this line doesn't work, because operator+ returns ADS<DerType&>, which then cannot be converted to ADS<DerType> const AD denom = chi_3 + _cv1_3; return 0; } I'm not sure what the intent is for operator+ (and -) to return ADS<DerType&> (probably to reuse the original derivatives?), but then the conversion from ADS<DerType&> to ADS<DerType> doesn't seem allowed, the intended constructor fails due to the unexpected reference in OtherDerType.
Applying the following patch seems to work around the problem for me: --- a/AutoDiffScalar.h 2016-05-10 04:24:55.000000000 +0200 +++ b/AutoDiffScalar.h 2016-05-10 16:47:36.000000000 +0200 @@ -101,7 +101,7 @@ template<typename OtherDerType> AutoDiffScalar(const AutoDiffScalar<OtherDerType>& other #ifndef EIGEN_PARSED_BY_DOXYGEN - , typename internal::enable_if<internal::is_same<Scalar,typename OtherDerType::Scalar>::value,void*>::type = 0 + , typename internal::enable_if<internal::is_same<Scalar, typename Eigen::internal::traits<typename Eigen::internal::remove_all<DerType>::type>::Scalar>::value,void*>::type = 0 #endif ) : m_value(other.value()), m_derivatives(other.derivatives())
Thanks for the patch, but it should be OtherDerType instead of DerType. Also, this issue applies to 3.3 only. Fix: https://bitbucket.org/eigen/eigen/commits/e6a5d4ea379c Backport of the unit test to 3.2: https://bitbucket.org/eigen/eigen/commits/638f9632e24c
Ah yes, I had taken the most recent AutoDiffScalar from the default branch to get the fix to http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1189 which might be why I saw this problem using an otherwise vanilla Eigen 3.2. Thanks!
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