3方差的专业定义是随机变量的二次中心矩，与期望值之差的平方的加权平均值。

The technical definition of variance is the random variable's second central moment, the weighted average of the square of the differences from the expected value.

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本文给出了化不含平方项的两类特殊二次型为标准形的一种直接选取满秩线性变换法。

The paper teus a direct way to select nonsingular linear transformation by changing two special quadratic forms without square terms to the standard form.

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引用矩阵的有关理论，给出了平方和分解式中二次型秩数的计算方法。

By introducing theories of matrix, this paper presents a calculation method for the rank of the quadratic form in quadratic sum resolution.

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We've seen log, we've seen linear, we've seen quadratic, we've seen exponential.

我们看过了对数级的，线性的，二次平方的，指数级的算法。

麻省理工公开课 - 计算机科学及编程导论课程节选

It is certainly possible, for example, that a quadratic algorithm could run faster than a linear algorithm. It depends on what the input is, it depends on, you know, what the particular cases are. So it is not the case that, on every input, a linear algorithm is always going to be better than a quadratic algorithm.

一个二次平方级复杂度的算法,当然也是可能跑的比线性复杂度算法快的,这取决于，你知道的，输入以及特定的案例，因此并不是对于每个输入,线性复杂度就一定会,比二次平方级复杂度的算法的表现要好,只是通常来说是这样的。

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