def construct_optimizer()

in slowfast/models/optimizer.py [0:0]
79 lines of code
19 McCabe index (conditional complexity)

def construct_optimizer(model, cfg):
    """
    Construct a stochastic gradient descent or ADAM optimizer with momentum.
    Details can be found in:
    Herbert Robbins, and Sutton Monro. "A stochastic approximation method."
    and
    Diederik P.Kingma, and Jimmy Ba.
    "Adam: A Method for Stochastic Optimization."

    Args:
        model (model): model to perform stochastic gradient descent
        optimization or ADAM optimization.
        cfg (config): configs of hyper-parameters of SGD or ADAM, includes base
        learning rate,  momentum, weight_decay, dampening, and etc.
    """
    bn_parameters = []
    non_bn_parameters = []
    zero_parameters = []
    no_grad_parameters = []
    skip = {}
    if cfg.NUM_GPUS > 1:
        if hasattr(model.module, "no_weight_decay"):
            skip = model.module.no_weight_decay()
            skip = {"module." + v for v in skip}
    else:
        if hasattr(model, "no_weight_decay"):
            skip = model.no_weight_decay()

    for name, m in model.named_modules():
        is_bn = isinstance(m, torch.nn.modules.batchnorm._NormBase)
        for p in m.parameters(recurse=False):
            if not p.requires_grad:
                no_grad_parameters.append(p)
            elif is_bn:
                bn_parameters.append(p)
            elif name in skip:
                zero_parameters.append(p)
            elif cfg.SOLVER.ZERO_WD_1D_PARAM and \
                (len(p.shape) == 1 or name.endswith(".bias")):
                zero_parameters.append(p)
            else:
                non_bn_parameters.append(p)

    optim_params = [
        {"params": bn_parameters, "weight_decay": cfg.BN.WEIGHT_DECAY},
        {"params": non_bn_parameters, "weight_decay": cfg.SOLVER.WEIGHT_DECAY},
        {"params": zero_parameters, "weight_decay": 0.0},
    ]
    optim_params = [x for x in optim_params if len(x["params"])]

    # Check all parameters will be passed into optimizer.
    assert len(list(model.parameters())) == len(non_bn_parameters) + len(
        bn_parameters
    ) + len(zero_parameters) + len(
        no_grad_parameters
    ), "parameter size does not match: {} + {} + {} + {} != {}".format(
        len(non_bn_parameters),
        len(bn_parameters),
        len(zero_parameters),
        len(no_grad_parameters),
        len(list(model.parameters())),
    )
    print(
        "bn {}, non bn {}, zero {} no grad {}".format(
            len(bn_parameters),
            len(non_bn_parameters),
            len(zero_parameters),
            len(no_grad_parameters),
        )
    )

    if cfg.SOLVER.OPTIMIZING_METHOD == "sgd":
        return torch.optim.SGD(
            optim_params,
            lr=cfg.SOLVER.BASE_LR,
            momentum=cfg.SOLVER.MOMENTUM,
            weight_decay=cfg.SOLVER.WEIGHT_DECAY,
            dampening=cfg.SOLVER.DAMPENING,
            nesterov=cfg.SOLVER.NESTEROV,
        )
    elif cfg.SOLVER.OPTIMIZING_METHOD == "adam":
        return torch.optim.Adam(
            optim_params,
            lr=cfg.SOLVER.BASE_LR,
            betas=(0.9, 0.999),
            weight_decay=cfg.SOLVER.WEIGHT_DECAY,
        )
    elif cfg.SOLVER.OPTIMIZING_METHOD == "adamw":
        return torch.optim.AdamW(
            optim_params,
            lr=cfg.SOLVER.BASE_LR,
            eps=1e-08,
            weight_decay=cfg.SOLVER.WEIGHT_DECAY,
        )
    else:
        raise NotImplementedError(
            "Does not support {} optimizer".format(cfg.SOLVER.OPTIMIZING_METHOD)
        )