fcfit - simplifying flat+cosine anneal

fcfit.py

@@ -0,0 +1,23 @@
+#flat and cosine annealer - @mgrankin invented
+#let's make it fast and easy - @lessw2020
+
+def fcfit(learn, num_epoch=2, lr=4e-3, start_pct=.72, f_show_curve=True):
+    if num_epoch<1:
+        raiseValueError("num_epoch must be 1 or higher")
+    n = len(learn.data.train_dl)
+    anneal_start = int(n*num_epoch*start_pct) #compute what batch to start
+    batch_finish = (n*num_epoch - anneal_start)
+    phase0 = TrainingPhase(anneal_start).schedule_hp('lr', lr)
+    phase1 = TrainingPhase(n*5 - anneal_start).schedule_hp('lr', lr, anneal=annealing_cos)
+    phases = [phase0, phase1]
+    sched = GeneralScheduler(learn, phases)
+    #save the setup
+    learn.callbacks.append(sched)
+    #start the training
+    print(f"fcfit: num_epochs: {num_epoch}, lr = {lr}") 
+    print(f"Flat for {anneal_start} epochs, then cosine anneal for {batch_finish}")
+    learn.fit(num_epoch)
+    #bonus -show lr curve?
+    if f_show_curve:    
+        learn.recorder.plot_lr()    
+