﻿功能:双伽马函数求值

格式:Digamma(a)

说明:
1、a为数据或者矩阵变量,当为矩阵变量时,对矩阵里每一个元素进行操作.
2、本函数求如下值
$$
\mathbf{Digamma}(a) = \dfrac{\Gamma'(a)}{\Gamma(a)}
$$


参考:{双伽马函数<http://zh.wikipedia.org/wiki/%E5%8F%8C%E4%BC%BD%E7%8E%9B%E5%87%BD%E6%95%B0>}.

例子:

a =
[ 9.94500462428900     61.4225915919163     61.5795303888524     98.3220250803614
  47.6583924366433     48.3697384355449     68.7553858238996     82.3566885117240
  83.6785498930507     94.6295160309549     41.7823175628587     38.0703375386402
  37.7239077993314     36.1639799718577     27.1439382467158     93.7976213143196 ]

b = digamma(a)//回车后得到如下结果
b = 
[ 2.24595215226641    4.10961529367808    4.11218795990197    4.58315411119795
  3.85353072191754    3.86850172098972    4.22326528743865    4.40497623543924
  4.42099552300078    4.54467636654665    3.72045870857152    3.62624435893786
  3.61698130461779    3.57417396944677    3.28262034613053    4.53579939923441 ]