 How to use  Here is how to use this model in PyTorch to perform unconditional image generation:  ```python from transformers import ImageGPTFeatureExtractor, ImageGPTForCausalImageModeling import torch import matplotlib.pyplot as plt import numpy as np  feature_extractor = ImageGPTFeatureExtractor.from_pretrained('openai/imagegpt-small') model = ImageGPTForCausalImageModeling.from_pretrained('openai/imagegpt-small')  device = torch.device("cuda" if torch.cuda.is_available() else "cpu") model.to(device)  