(self, gamma=2.0, alpha=0.25)
Constructor.

    Args:
      gamma: exponent of the modulating factor (1 - p_t) ^ gamma.
      alpha: optional alpha weighting factor to balance positives vs negatives.
      all_zero_negative: bool. if True, will treat all zero as background.
        else, will treat first label as background. only affect alpha.
Constructor.
Constructor .
def __init__(self, gamma=2.0, alpha=0.25):
    """Constructor.

    Args:
      gamma: exponent of the modulating factor (1 - p_t) ^ gamma.
      alpha: optional alpha weighting factor to balance positives vs negatives.
      all_zero_negative: bool. if True, will treat all zero as background.
        else, will treat first label as background. only affect alpha.
    """
    self._alpha = alpha
    self._gamma = gamma
def __init__ ( self , gamma = 2.0 , alpha = 0.25 ) : self . _alpha = alpha self . _gamma = gamma