code: def cost(z):
      """Compute cost."""
      num_tr_data_to_use = _get_tr_dataset_size_from_z0(z[0])
      return (num_tr_data_to_use / float(MAX_TR_DATA_SIZE)) ** 3
  
imports: import numpy
  import pickle
  from salsa_estimator import salsa_train_and_validate
label_desc: Use image node_id 4 for calling a global function with example usage: cost(z) and returns: unknown