定义了n重导数，n元绝对连续函数，广义n重原函数及牛顿n重积分。

It defines n-ple derivative, n-ary absolutely continuous function, generalized n-ple primitive function and Newton n-ple integral.

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在边界提取时选取有一定间距的像素分别计算三原色梯度，把其中绝对值最大的梯度作为边界存在的判据之一，同时根据二阶导数符号变化提取边界。

Third, the gradient between two pixels that have certain distance was calculated in three color components respectively, and then the maximum of gradients of the three was attained.

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