num::solvable_field

Defined in header <fields/concepts.hpp>

template <class F, class T = real, class V = vec<real>>
concept solvable_field = scalar_field_like<F, T> && vec_field<F, V>;

field whose storage satisfies the vector space contract.

This is what lets an implicit time stepper solve on a field directly. It is exactly num::vec_field restricted to fields sampled on a grid, so it refines that rather than restating the requirement — and, like it, takes the space as a parameter instead of naming vec<real>.