Bug 1760

Created attachment 956 [details]
Minimal failing example

In the test.cpp file in the attachment, I have followed your explanation here about how to add support for Adolc's adtl::adouble type: http://eigen.tuxfamily.org/dox/TopicCustomizing_CustomScalar.html . The code compiles under the version of Eigen that comes with Ubuntu 16.04 (dpkg calls this version 3.3~beta1-2), but when I compile it under Eigen 3.3.7, the fact that I have multiplied a double with an Eigen::Matrix<adtl::adouble,2,1> causes compiler errors. I first noticed this issue in Eigen 3.3.4 (the version that comes with Ubuntu 18.04). But if you replace adtl::adouble with std::complex<double>, it compiles in all three versions of Eigen. The attachment contains the GCC errors that occur under Eigen 3.3.4 and 3.3.7.

Adolc provides the following overload of the * operator:

adouble operator * (const double v, const adouble& a) 

Do I need to specialise some additional class templates to allow Eigen to determine the return type? 

P.S.: I know I can work around the issue by constructing an adtl::adouble from the double.
P.P.S.: I'm using AdolC 2.4.1, but I don't think this is relevant to the issue.