Source code for lmflow.optim.lars

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import torch
from torch.optim.optimizer import Optimizer

[docs] class LARS(Optimizer): r"""Extends SGD in PyTorch with LARS scaling from the paper `Large batch training of Convolutional Networks`__. .. note:: The application of momentum in the SGD part is modified according to the PyTorch standards. LARS scaling fits into the equation in the following fashion. .. math:: \begin{aligned} g_{t+1} & = \text{lars_lr} * (\beta * p_{t} + g_{t+1}), \\ v_{t+1} & = \\mu * v_{t} + g_{t+1}, \\ p_{t+1} & = p_{t} - \text{lr} * v_{t+1}, \\end{aligned} where :math:`p`, :math:`g`, :math:`v`, :math:`\\mu` and :math:`\beta` denote the parameters, gradient, velocity, momentum, and weight decay respectively. The :math:`lars_lr` is defined by Eq. 6 in the paper. The Nesterov version is analogously modified. .. warning:: Parameters with weight decay set to 0 will automatically be excluded from layer-wise LR scaling. This is to ensure consistency with papers like SimCLR and BYOL. __ https://arxiv.org/pdf/1708.03888.pdf Note: Reference code: https://github.com/PyTorchLightning/lightning-bolts/ """ def __init__( self, params, lr: float = 1e-2, momentum: float = 0.0, dampening: float = 0.0, weight_decay: float = 0.0, nesterov: bool = False, trust_coefficient: float = 0.01, eps: float = 1e-8, ): if lr <= 0.0: raise ValueError("Invalid learning rate: {}".format(lr)) if eps < 0.0: raise ValueError("Invalid epsilon value: {}".format(eps)) if momentum < 0.0: raise ValueError("Invalid momentum value: {}".format(momentum)) if dampening < 0.0: raise ValueError("Invalid dampening value: {}".format(dampening)) if weight_decay < 0.0: raise ValueError( "Invalid weight_decay value: {}".format(weight_decay) ) if trust_coefficient < 0.0: raise ValueError( "Invalid trust_coefficient value: {}".format(trust_coefficient) ) defaults = dict( lr=lr, momentum=momentum, dampening=dampening, weight_decay=weight_decay, nesterov=nesterov, trust_coefficient=trust_coefficient, eps=eps, ) if nesterov and (momentum <= 0 or dampening != 0): raise ValueError( "Nesterov momentum requires a momentum and zero dampening" ) super().__init__(params, defaults)
[docs] def __setstate__(self, state) -> None: super().__setstate__(state) for group in self.param_groups: group.setdefault("nesterov", False)
@torch.no_grad()
[docs] def step(self, closure = None): r"""Performs a single optimization step. Arguments: closure: A closure that reevaluates the model and returns the loss. """ loss = None if closure is not None: with torch.enable_grad(): loss = closure() # exclude scaling for params with 0 weight decay for group in self.param_groups: weight_decay = group["weight_decay"] momentum = group["momentum"] dampening = group["dampening"] nesterov = group["nesterov"] for p in group["params"]: if p.grad is None: continue d_p = p.grad p_norm = torch.norm(p.data) g_norm = torch.norm(p.grad.data) # lars scaling + weight decay part if weight_decay != 0: if p_norm != 0 and g_norm != 0: lars_lr = p_norm / ( g_norm + p_norm * weight_decay + group["eps"] ) lars_lr *= group["trust_coefficient"] d_p = d_p.add(p, alpha=weight_decay) d_p *= lars_lr if momentum != 0: param_state = self.state[p] if "momentum_buffer" not in param_state: buf = param_state["momentum_buffer"] = torch.clone( d_p ).detach() else: buf = param_state["momentum_buffer"] buf.mul_(momentum).add_(d_p, alpha=1 - dampening) if nesterov: d_p = d_p.add(buf, alpha=momentum) else: d_p = buf p.add_(d_p, alpha=-group["lr"]) return loss