class_docstr: A basic step function
  
  Values at the ends are handled in the simplest way possible: everything to
  the left of ``x[0]`` is set to `ival`; everything to the right of ``x[-1]``
  is set to ``y[-1]``.
  
  Examples
  --------
  >>> x = np.arange(20)
  >>> y = np.arange(20)
  >>> f = StepFunction(x, y)
  >>>
  >>> f(3.2)
  3.0
  >>> res = f([[3.2, 4.5],[24, -3.1]])
  >>> np.all(res == [[ 3, 4],
  ...                [19, 0]])
  True
code: def __call__(self, time):
      tind = np.searchsorted(self.x, time) - 1
      return self.y[tind]
  
file_path: nipy/nipy/algorithms/statistics/models/utils.py
imports: import numpy
  import scipy.interpolate
label_desc: Use image node_id 2 for calling the StepFunction obj's underlying member method code with example usage: obj.__call__(time) and returns: self