code: def sigmoid(x, L, x0, k, b):
      y = L / (1 + np.exp(-k * (x - x0))) + b
      return y
  
file_path: scattertext/scattertext/smoothing/sigmoidal.py
imports: import numpy
  from scipy.optimize import curve_fit
label_desc: Use image node_id 1 for calling a global function with example usage: sigmoid(x, L, x0, k, b) and returns: y