A diversity index is a quantitative measure that reflects how many different types (such as species)there are in a dataset, and simultaneously takes into account how evenly the basic entities (such as individuals) are distributed among those types. The value of a diversity index increases both when the number of types increases and when evenness increases. For a given number of types, the value of a diversity index is maximized when all types are equally abundant. (https://en.wikipedia.org/wiki/Diversity_index) (多样性指数是一个定量的描述，主要关注菌的种类以及菌的含量分布)

   多样性指数有3类，分别是alpha、beta和gamma指数，3个指数之间的关系如下： The term alpha diversity(α-diversity) was introduced by R. H. Whittaker together with the terms beta diversity (β-diversity) and gamma diversity (γ-diversity). Whittaker's idea was that the total species diversity in a landscape (gamma diversity) is determined by two different things, the mean species diversity in sites or habitats at a more local scale (alpha diversity) and the differentiation among those habitats (beta diversity). (https://en.wikipedia.org/wiki/Alpha_diversity)

   针对alpha diversity，是用于测量群落内生物种类数量以及生物种类间相对丰度的一种测量。它反映了群落内物种间通过竞争资源或利用同种生境而产生的共存结果，可分为物种丰富度指数、物种均匀度指数、物种多样性指数三类。(http://blog.sina.com.cn/s/blog_670445240101m9sb.html、http://www.coloss.org/beebook/I/gut-symbionts/2/2/4)

    sobs的计算为The sobs calculator returns the number ofobserved OTUs for an OTU definition.

    Chao的计算公式为：

   shannon index的计算公式为：

   Simpson index的计算公式为：