Scalar and vector-valued expression

Question

Hi,
I 'm using c++ dolfin.
I was wondering if

 Expression ()

and

 Expression(1)

initialize the same object or not. Because I would expect that a vector-valued expression of dimension 1 should be the same as a scalar expression, but I'm getting some error if I use the latter in a scalar problem.

Answer 1

It is not the same because scalar is rank 0 and vector is rank 1. Of course you can appropriately convert between them. On UFL level

vector = as_vector((scalar,))
scalar = vector[0]