计算F1Score

predictions = pval < epsilon
fp = sum((predictions == 1) & (y == 0))
fn = sum((predictions == 0) & (y == 1))
tp = sum((predictions == 1) & (y == 1))
precision = tp / (tp + fp)
recall = tp / (tp + fn)
F1 = 2 * precision * recall / (precision + recall)