Loads checkpoint from filename.

        :param filename: path to the checkpoint file

def load(self, filename):
        """
        Loads checkpoint from filename.

        :param filename: path to the checkpoint file
        """
        if os.path.isfile(filename):
            checkpoint = torch.load(filename, map_location={'cuda:0': 'cpu'})
            if self.distributed:
                self.model.module.load_state_dict(checkpoint['state_dict'])
            else:
                self.model.load_state_dict(checkpoint['state_dict'])
            self.fp_optimizer.initialize_model(self.model)
            self.optimizer.load_state_dict(checkpoint['optimizer'])
            self.scheduler.load_state_dict(checkpoint['scheduler'])
            self.epoch = checkpoint['epoch']
            self.loss = checkpoint['loss']
            logging.info(f'Loaded checkpoint {filename} (epoch {self.epoch})')
        else:
            logging.error(f'Invalid checkpoint: {filename}')