CostWrapper could/should be a function, not a class

[ilectra]

No data in it is used/called on its own, it's only used to calculate the cost once.

[jgomezdans]

In a way. However if using trust-krylov function minimiser in scipy, the idea of CostWrappre is to cache common calculations for the cost function, its Jacobian and the hessianp (hessian times product). Check pr1

[jgomezdans]

See also #2