调和级数近似求和公式推导

调和级数(Harmonic series)是一个发散的无穷级数

\sum_{i=1}^{n}\frac{1}{i}=ln(n) +\gamma

其中\gamma 为欧拉常数, \gamma=\lim_{n \rightarrow \infty}\int_1^n(\frac{1}{\lfloor x \rfloor} - \frac{1}{x})dx \approx 0.577215664....

推导过程:

\begin{aligned} \sum_{i=1}^{n} \frac{1}{i} &= \sum_{i=1}^{n} \int_i^{i+1} \frac{1}{\lfloor x \rfloor}dx \\ &= \int_{1}^{n+1}(\frac{1}{x} + (\frac {1}{\lfloor x \rfloor} - \frac{1}{x}))dx \\&= \int_1^{n+1}\frac{1}{x}dx +\int_i^{n+1}(\frac{1}{\lfloor x \rfloor}- \ \frac{1}{x}) dx \\ &\approx ln(n+1)+\gamma \end{aligned}

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转载自blog.csdn.net/u010622506/article/details/83039816
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