def load_model(hparams):
    model = Tacotron2(hparams).cuda()
    if hparams.fp16_run:
        model.decoder.attention_layer.score_mask_value = finfo('float16').min

    if hparams.distributed_run:
        model = apply_gradient_allreduce(model)

    return model
def train(output_directory, log_directory, checkpoint_path, warm_start, n_gpus,
          rank, group_name, hparams):
    """Training and validation logging results to tensorboard and stdout

    Params
    ------
    output_directory (string): directory to save checkpoints
    log_directory (string) directory to save tensorboard logs
    checkpoint_path(string): checkpoint path
    n_gpus (int): number of gpus
    rank (int): rank of current gpu
    hparams (object): comma separated list of "name=value" pairs.
    """
    if hparams.distributed_run:
        init_distributed(hparams, n_gpus, rank, group_name)

    torch.manual_seed(hparams.seed)
    torch.cuda.manual_seed(hparams.seed)

    model = load_model(hparams)
    learning_rate = hparams.learning_rate
    optimizer = torch.optim.Adam(model.parameters(),
                                 lr=learning_rate,
                                 weight_decay=hparams.weight_decay)

    if hparams.fp16_run:
        from apex import amp
        model, optimizer = amp.initialize(model, optimizer, opt_level='O2')

    if hparams.distributed_run:
        model = apply_gradient_allreduce(model)

    criterion = Tacotron2Loss()

    logger = prepare_directories_and_logger(output_directory, log_directory,
                                            rank)

    train_loader, valset, collate_fn = prepare_dataloaders(hparams)

    # Load checkpoint if one exists
    iteration = 0
    epoch_offset = 0
    if checkpoint_path is not None:
        if warm_start:
            model = warm_start_model(checkpoint_path, model,
                                     hparams.ignore_layers)
        else:
            model, optimizer, _learning_rate, iteration = load_checkpoint(
                checkpoint_path, model, optimizer)
            if hparams.use_saved_learning_rate:
                learning_rate = _learning_rate
            iteration += 1  # next iteration is iteration + 1
            epoch_offset = max(0, int(iteration / len(train_loader)))

    model.train()
    is_overflow = False
    # ================ MAIN TRAINNIG LOOP! ===================
    for epoch in range(epoch_offset, hparams.epochs):
        print("Epoch: {}".format(epoch))
        for i, batch in enumerate(train_loader):
            start = time.perf_counter()
            for param_group in optimizer.param_groups:
                param_group['lr'] = learning_rate

            model.zero_grad()
            x, y = model.parse_batch(batch)
            y_pred = model(x)

            loss = criterion(y_pred, y)
            if hparams.distributed_run:
                reduced_loss = reduce_tensor(loss.data, n_gpus).item()
            else:
                reduced_loss = loss.item()
            if hparams.fp16_run:
                with amp.scale_loss(loss, optimizer) as scaled_loss:
                    scaled_loss.backward()
            else:
                loss.backward()

            if hparams.fp16_run:
                grad_norm = torch.nn.utils.clip_grad_norm_(
                    amp.master_params(optimizer), hparams.grad_clip_thresh)
                is_overflow = math.isnan(grad_norm)
            else:
                grad_norm = torch.nn.utils.clip_grad_norm_(
                    model.parameters(), hparams.grad_clip_thresh)

            optimizer.step()

            if not is_overflow and rank == 0:
                duration = time.perf_counter() - start
                print(
                    "Train loss {} {:.6f} Grad Norm {:.6f} {:.2f}s/it".format(
                        iteration, reduced_loss, grad_norm, duration))
                logger.log_training(reduced_loss, grad_norm, learning_rate,
                                    duration, iteration)

            if not is_overflow and (iteration % hparams.iters_per_checkpoint
                                    == 0):
                validate(model, criterion, valset, iteration,
                         hparams.batch_size, n_gpus, collate_fn, logger,
                         hparams.distributed_run, rank)
                if rank == 0:
                    checkpoint_path = os.path.join(
                        output_directory, "checkpoint_{}".format(iteration))
                    save_checkpoint(model, optimizer, learning_rate, iteration,
                                    checkpoint_path)

            iteration += 1