[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify code snippets into one of the following categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']."}, {'role': 'user', 'content': 'Identify the single most appropriate category to which the provided code belongs. Provide your response as a single category label without any additional information, commentary, or personal opinions.\\nPython Code:cov_matrix=np.cov(returns)\ndiag=cov_matrix.diagonal()\ndiag_matrix=np.diag(np.diag(cov_matrix))\ngarch11 = arch_model(diag, p=1, q=1)\nres = garch11.fit(update_freq=10)\nalpha=res.params[2]\nbeta=res.params[3]\nesubt.append(np.matmul(np.linalg.inv(diag_matrix),returns))\nq_list.append(np.ones((stock_returns.size,stock_returns.size)))\npred_cov=[]\nnew_returns=[]'}, {'role': 'assistant', 'content': 'modelling'}]