class_docstr: Sigmoid activation function.
class_docstr_tok: ["Sigmoid","activation","function","."]
code: def apply(z):
      return 1 / (1 + np.exp(-z))
  
file_path: river/river/neural_net/activations.py
imports: from __future__ import annotations
  import abc
  import numpy
label_desc: Use image node_id 1 for calling the Sigmoid obj's underlying member method code with example usage: obj.apply(z) and returns: unknown