(self, sample)
Evaluate cost function and derivatives.
        Args:
            sample:  A single sample.
Evaluate cost function and derivatives.
        Args:
            sample:  A single sample.
Evaluate cost function and derivatives . Args : sample : A single sample .
def eval(self, sample):
        """
        Evaluate cost function and derivatives.
        Args:
            sample:  A single sample.
        """
        raise NotImplementedError("Must be implemented in subclass.")
def eval ( self , sample ) : raise NotImplementedError ( "Must be implemented in subclass." )