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correct copysign backward #74322

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Merged
lshpku merged 2 commits into from
Aug 11, 2025
Merged

correct copysign backward #74322

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0396694
correct copysign backward
wangyuwen1999 Jul 30, 2025
d314fc3
correct codestyle
wangyuwen1999 Aug 8, 2025
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2 changes: 1 addition & 1 deletion paddle/phi/kernels/funcs/elementwise_functor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1378,7 +1378,7 @@ struct CopySignGradXYFunctor {
if (x == static_cast<InT>(0))
outs[0] = static_cast<OutT>(0);
else
outs[0] = static_cast<OutT>(dout * (funcs::copysign_func(x, y)) / x);
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@lshpku lshpku Jul 31, 2025

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这样改有依据吗？比如看下torch是这样改的吗？我怎么感觉这样改虽然解决了下溢问题但可能带来新的精度问题

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@wangyuwen1999 wangyuwen1999 Jul 31, 2025

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这样修改的一个依据是这个kernel的原作者针对copysign的反向写了3个GradFunctor，在CopySignGradXFunctor和CopySignGradXYFunctor中，对于x的求导顺序出现了差别，说明是作者在编程时错写了CopySignGradXYFunctor针对X的求导，将右括号放错了位置。
0d15166e28aa20c32dfbb2231387601c
当然，我们可以参考torch的实现。
383a79de6fc6ddd98f7f7e64e34a722b
同样是先除再乘。

outs[0] = static_cast<OutT>(dout * (funcs::copysign_func(x, y) / x));
// dy = 0
outs[1] = static_cast<OutT>(0);
return outs;
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