code: def jump(x, mid):
      """Heaviside step function."""
      o = np.zeros(x.size)
      imid = max(np.where(x <= mid)[0])
      o[imid:] = 1.0
      return o
  
imports: import matplotlib.pyplot
  import numpy
  from lmfit import CompositeModel, Model
  from lmfit.lineshapes import gaussian, step
label_desc: Use image node_id 1 for calling a global function with example usage: jump(x, mid) and returns: o