def _der(self, *args):
    '\n        Evaluate the derivative of the function.  The first input must exist and should be an array.\n        Returns an array of identical shape to args[0] (if it exists).  This is an array of zeros.\n        '
    if (len(args) > 0):
        if _isscalar(args[0]):
            return 0.0
        else:
            shape = args[0].shape
            return np.zeros(shape)
    else:
        return 0.0
Evaluate the derivative of the function.  The first input must exist and should be an array.
Returns an array of identical shape to args[0] (if it exists).  This is an array of zeros.
def _der(self, *args):
    '\n        Evaluate the derivative of the function.  The first input must exist and should be an array.\n        Returns an array of identical shape to args[0] (if it exists).  This is an array of zeros.\n        '
    if (len(args) > 0):
        if _isscalar(args[0]):
            return 0.0
        else:
            shape = args[0].shape
            return np.zeros(shape)
    else:
        return 0.0