﻿功能:双伽马函数求值

格式:Digamma(a)

说明: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.
关于:双伽马函数Digamma(a)=Γ'(a)/Γ(a),关于更详细的情况请参看维基百科{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 ]

digamma(a)//回车后得到如下结果
ans =
[ 2.24608625252403     4.10956645649446     4.11222737484554     4.58313130597108
  3.85356459275036     3.86844921497587     4.22323463823182     4.40492860126336
  4.42101957931860     4.54471863498437     3.72040971097916     3.62609262047840
  3.61697467893091     3.57417436207408     3.28256007904991     4.53574231826759 ]

digamma(0.123456)//回车后得到如下结果
ans =
[ -8.4907907487013 ]

//By 2012/6/15