class_docstr: Forrester function. 
  
  :param sd: standard deviation, to generate noisy evaluations of the function.
code: def __init__(self, sd=None):
      self.input_dim = 1
      if sd == None:
          self.sd = 0
      else:
          self.sd = sd
      self.min = 0.78  ## approx
      self.fmin = -6  ## approx
      self.bounds = [(0, 1)]
  
imports: import matplotlib.pyplot
  import numpy
label_desc: Use image node_id 1 to create a new forrester object from inherited base classes: function1d with example: obj = forrester(sd)