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fix(math/poly/fft.md): typo #3111

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Apr 14, 2021
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fix(math/poly/fft.md): typo #3111

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2 changes: 1 addition & 1 deletion docs/math/poly/fft.md
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Expand Up @@ -307,7 +307,7 @@ $$
\frac{1}{\omega_k}=\omega_k^{-1}=e^{-\frac{2\pi i}{k}}=\cos\left(\frac{2\pi}{k}\right)+i\cdot \sin\left(-\frac{2\pi}{k}\right)
$$

因此我们可以尝试着把单位根 $\omega_k$ 取成 $e^{-\frac{2\pi i}{k}}$，这样我们的计算结果就会变成原来的倒数，而其它的操作过程与 DFT 是完全相同的。我们可以定义一个函数，在里面加一个参数 $1$ 或者是 $-1$，然后把它乘到 $\pi$ $的身上。传入$ 1 $就是 DFT，传入$-1$ 就是 IDFT。
因此我们可以尝试着把单位根 $\omega_k$ 取成 $e^{-\frac{2\pi i}{k}}$，这样我们的计算结果就会变成原来的倒数，而其它的操作过程与 DFT 是完全相同的。我们可以定义一个函数，在里面加一个参数 $1$ 或者是 $-1$，然后把它乘到 $\pi$ 上。传入 $1$ 就是 DFT，传入 $-1$ 就是 IDFT。

### 单位复根周期性

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