Function minimize_tr 

pub fn minimize_tr<P: TrustRegionProblem, S: SubproblemStep>(
    problem: &mut P,
    step: &S,
    cfg: &TrustRegionConfig,
) -> Report

Minimise ½‖r(p)‖² over the free parameters of problem with an explicit Δ-radius trust region, delegating the per-iteration subproblem to step.

On return the problem holds the best parameters found. Deterministic: no RNG, no clock — identical inputs give identical iterates — given a fixed faer parallelism policy; spectrafit-solver::fit sets Par::Seq for the whole fit, and a caller that leaves faer on its default (potentially multi-threaded) policy can see floating-point summation-order differences across runs.