code: def fit_flat_cos(
      self: Learner,
      n_epoch,
      lr=None,
      div_final=1e5,
      pct_start=0.75,
      wd=None,
      cbs=None,
      reset_opt=False,
      start_epoch=0,
  ):
      "Fit `self.model` for `n_epoch` at flat `lr` before a cosine annealing."
      if self.opt is None:
          self.create_opt()
      self.opt.set_hyper("lr", self.lr if lr is None else lr)
      lr = np.array([h["lr"] for h in self.opt.hypers])
      scheds = {"lr": combined_cos(pct_start, lr, lr, lr / div_final)}
      self.fit(
          n_epoch,
          cbs=ParamScheduler(scheds) + L(cbs),
          reset_opt=reset_opt,
          wd=wd,
          start_epoch=0,
      )
  
imports: from __future__ import annotations
  from ..basics import *
  from .tracker import SaveModelCallback
label_desc: Use image node_id 15 for calling a global function with example usage: fit_flat_cos(n_epoch, lr, div_final, pct_start, wd, cbs, reset_opt, start_epoch) without return types