code: def _ncdf(x):
      return (tf.math.erf(x / _SQRT_2) + 1) / 2
  
file_path: tf-quant-finance/tf_quant_finance/black_scholes/vanilla_prices.py
imports: import numpy
  import tensorflow.compat.v2
  from tf_quant_finance import types
label_desc: Use image node_id 6 for calling a global function with example usage: _ncdf(x) and returns: unknown