全球粮食贸易网络演变及其驱动因素解析

管靖, 宋周莺, 刘卫东

Change of the global grain trade network and its driving factors

GUAN Jing, SONG Zhouying, LIU Weidong

表2 泊松分布、负二项分布的定义及意义

Tab.2 Definitions and meanings of Poisson distribution and negative binomial distribution

分布	定义	累积分布函数	意义
泊松分布 $X ~ P (p)$	$P (X = w) = \frac{p^{w}}{w!} e^{- p}$	$P (X \leq w) = \{\begin{array}{l} \overset{w}{\sum_{i = 0}} \frac{p^{i}}{i!} e^{- p} (w \geq 0) \\ 0 (w < 0) \end{array}$	在一段固定长度的时间中,O地和D地间发生的贸易规模为 $w$
负二项分布 $X ~ N B (r, p)$	$P (X = W) = (\begin{array}{l} W - 1 \\ r - 1 \end{array}) p^{r} {(1 - p)}^{W - r}$	$P (X \leq W) = \{\begin{array}{l} \overset{W}{\sum_{i = 0}} (\begin{array}{l} i - 1 \\ r - 1 \end{array}) p^{r} {(1 - p)}^{i - r} (W \geq r) \\ 0 (W < r) \end{array}$	O和D地间存在一定贸易规模 $r$ 时,网络全部贸易规模为 $W$