Hi, can I request a feature?

I already like the eigen, but it would be nice, desirable, lovely, if the eigen had tensor notation with placeholders, like blitz + +. Is it difficult to implement it?

thanks,

Felipe.

It wouldn't be hard to code, and it could be done as a new, separate module (which you can start yourself).

However, the interest of doing this in Eigen, compared to Blitz, is limited by the fact that Eigen only does vectors and matrices, not higher-order tensors.

Hm and more worryingly, Eigen doesn't even know about the notion of covariant/contravariant, so, such a new module would first have to add this notion in a way that's syntactically convenient and doesn't incur code redundancy. It could for example define a new tensor class inheriting matrix and having a compile-time flag telling which indices are covariant/contravariant, and make sure that templated code that doesn't care about that isn't instantiated separately for each covariant/contravariant combination.