rue requires less nonlinear
        iterations, but more vector products. Only effective for method
        trust-krylov.

This function is called by the `minimize` function.
It is not supposed to be called directly.
Nz7Jacobian is currently required for trust-region methodsz_Either the Hessian or the Hessian-vector product is currently required for trust-region methodszBA subproblem solving strategy is required for trust-region methodsr