优点：输出在 (−1,1)，比 sigmoid 居中，对梯度更友好
get desiredSize() { return closed ? null : 1; },
。关于这个话题，雷电模拟器官方版本下载提供了深入分析
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添加图片注释，不超过 140 字（可选）
for t := range c {