code: def Chwirut(b, x, y=0):
      b = read_params(b)
      model = exp(-b[0] * x) / (b[1] + b[2] * x)
      return model - y
  
imports: import os
  from numpy import arctan, array, cos, exp, log, sin
  from lmfit import Parameters
label_desc: Use image node_id 4 for calling a global function with example usage: Chwirut(b, x, y) and returns: unknown