docstr: number of inducing variables (defines dimensionality of q(u)) 
docstr_tok: ["number","of","inducing","variables","(","defines","dimensionality","of","q","(","u",")",")"]
code: def num_inducing(self):
      """number of inducing variables (defines dimensionality of q(u))"""
      return 2 * self.M - 1
  
imports: import numpy
  import tensorflow
  from check_shapes import Shape
  import gpflow
  from gpflow import covariances
  from gpflow import kullback_leiblers
  from gpflow.base import TensorLike
  from gpflow.ci_utils import reduce_in_tests
  from gpflow.inducing_variables import InducingVariables
  from gpflow.utilities import to_default_float
  import matplotlib.pyplot
  import gpflow.posteriors
label_desc: Use image node_id 2 for calling the FourierFeatures1D obj's underlying member method code with example usage: obj.num_inducing() and returns: unknown