As @ChrisChiasson pointed out, that doesn’t seem to be enough no matter how we define the ScalarBinaryOpTraits. I think @ChrisChiasson tracked it down to an operation where with dynamic matrices, there is a cast of the second argument type to the first (or vice-versa) rather than casting up to the result type. When we have complex<double> and complex<var>, there’s no way to cast the second to the first. We don’t want to just literally support the cast because then we’d lose derivative information.