code: def ols_model_signature():
      return ModelSignature(
          inputs=Schema([TensorSpec(np.dtype("float64"), (-1, 3))]),
          outputs=Schema([TensorSpec(np.dtype("float64"), (-1,))]),
      )
  
imports: from collections import namedtuple
  import numpy
  import pandas
  import statsmodels.api
  from scipy.linalg import toeplitz
  from statsmodels.tsa.arima.model import ARIMA
  from statsmodels.tsa.arima_process import arma_generate_sample
  from mlflow.models import ModelSignature
  from mlflow.types.schema import Schema, TensorSpec
label_desc: Use image node_id 2 for calling a global function with example usage: ols_model_signature() and returns: ModelSignature