id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
4441	SFINAE for operator * breaking auto differentiation code	Jesse Perla <jesseperla@…>	Gunter	"A while back we had discussed adding overload resolution with SFINAE to the matrix/vector expressions involving scalars in order to implement operator*, etc. 
The choice was made to use is_convertible between the scalar and matrix type.

But this ended up breaking an auto-differentiation library (CPPAD) I was using.  Templated AD libraries will often have their own, arithmetic type which will record operations of the type * a double, etc. for a matrix multiplication by a scalar, etc. But you can't convert between them!

The basic change is to change from using is_convertible to using is_arithmetic.  A change to the result type is also needed for autodifferentation to work.

See the attached patch for the change to matrix/vector expression."	Bugs	new	Boost 1.44.0	uBLAS	Boost 1.44.0	Problem