code: def step() -> tf.Tensor:
      opt.minimize(model.training_loss, model.trainable_variables)
  
file_path: GPflow/doc/sphinx/notebooks/getting_started/parameters_and_their_optimisation.pct.py
imports: import os
  import warnings
  from typing import Optional
  import matplotlib.pyplot
  import numpy
  import pandas
  import tensorflow
  import tensorflow_probability
  from check_shapes import check_shapes
  from matplotlib.axes import Axes
  import gpflow
  from gpflow.ci_utils import is_continuous_integration
label_desc: Use image node_id 4 for calling a global function with example usage: step() without return types