Optimizer backwards compatibility (#1647)

Author: matthewdouglas

bitsandbytes/optim/optimizer.py

@@ -303,9 +303,9 @@ def get_config(self, gindex, pindex, group):
  config["eps"] = group["eps"]
  config["weight_decay"] = group["weight_decay"]
  config["lr"] = group["lr"]
- config["alpha"] = group.get("alpha")
- config["t_alpha"] = group.get("t_alpha")
- config["t_beta3"] = group.get("t_beta3")
+ config["alpha"] = group.get("alpha", 0.0)
+ config["t_alpha"] = group.get("t_alpha", 0)
+ config["t_beta3"] = group.get("t_beta3", 0)
  config["optim_bits"] = self.args.optim_bits
  config["min_8bit_size"] = self.args.min_8bit_size
  config["percentile_clipping"] = self.args.percentile_clipping
@@ -530,7 +530,7 @@ def update_step(self, group, p, gindex, pindex):
  state["state2"],
  config["betas"][1],
  config["betas"][2] if len(config["betas"]) >= 3 else 0.0,
- config["alpha"],
+ config.get("alpha", 0.0),
  config["weight_decay"],
  gnorm_scale,
  state["unorm_vec"] if config["max_unorm"] > 0.0 else None,
@@ -575,7 +575,7 @@ def update_step(self, group, p, gindex, pindex):
  config["betas"][0],
  config["betas"][1],
  config["betas"][2] if len(config["betas"]) >= 3 else 0.0,
- config["alpha"],
+ config.get("alpha", 0.0),
  config["eps"],
  step,
  config["lr"],