ncchi2_3.m

功能极全的GPS开发工具箱

%                             ncchi2_3.m
%  Scope:   This MATLAB macro computes the probability density function of the 
%           non-central chi-square distribution with three degrees of freedom.
%  Usage:   xoutput = ncchi2_3(x,lambda)
%  Description of parameters:
%           x       - input, scalar independent variable
%           lambda  - input, non-centrality parameter
%           xoutput - output, computed probability density function 
%  Remark:  This macro can be used for the computation of the integral of the
%           probability density function.
%  Last update:  04/12/00
%  Copyright (C) 1997-00 by LL Consulting. All Rights Reserved.

function  xoutput = ncchi2_3(x,lambda)

sum = 2./sqrt(pi);
temp = sum;

for k = 1:49
   termk = temp.*lambda.*x./(4.*k.*(k+0.5));
   sum = sum + termk;
   temp = termk;
end

a = 0.5/sqrt(2);
xoutput = a.*sum.*(exp(-0.5.*(x+lambda))).*(sqrt(x));