def P(y_true, y_pred):
    true_positives = K.sum(K.cast(K.greater(K.clip(y_true * y_pred, 0, 1), 0.20), 'float32'))
    pred_positives = K.sum(K.cast(K.greater(K.clip(y_pred, 0, 1), 0.20), 'float32'))
    precision = true_positives / (pred_positives + K.epsilon())
    return precision

def R(y_true, y_pred):
    true_positives = K.sum(K.cast(K.greater(K.clip(y_true * y_pred, 0, 1), 0.20), 'float32'))
    poss_positives = K.sum(K.cast(K.greater(K.clip(y_true, 0, 1), 0.20), 'float32'))
    recall = true_positives / (poss_positives + K.epsilon())
    return recall

def F(y_true, y_pred):
    p_val = P(y_true, y_pred)
    r_val = R(y_true, y_pred)
    f_val = 2*p_val*r_val / (p_val + r_val)
    return f_val