class_docstr: Rectified Linear Unit (ReLU) activation function.
class_docstr_tok: ["Rectified","Linear","Unit","(","ReLU",")","activation","function","."]
code: def gradient(z):
      a = np.zeros_like(z, dtype=z.dtype)
      a[z > 0] = 1
      return a
  
file_path: river/river/neural_net/activations.py
imports: from __future__ import annotations
  import abc
  import numpy
label_desc: Use image node_id 2 for calling the ReLU obj's underlying member method code with example usage: obj.gradient(z) and returns: a