Computes the GP-Lower Confidence Bound and its derivative

def _compute_acq_withGradients(self, x):
        """
        Computes the GP-Lower Confidence Bound and its derivative
        """
        m, s, dmdx, dsdx = self.model.predict_withGradients(x) 
        f_acqu = -m + self.exploration_weight * s       
        df_acqu = -dmdx + self.exploration_weight * dsdx
        return f_acqu, df_acqu