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2008-10-27 15:59 |
Matlab中超几何分布作图介绍
在用Matlab绘制各种常用概率分布的密度函数时，都比较简单，唯独超几何分布试了几次都不成功，输出结果总是 R*LPwJuv
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查看了一下帮助 help hygepdf ?W?n l:F
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HYGEPDF Hypergeometric probability density function. rSW{1o'
A C fhy[,
Y = HYGEPDF(X,M,K,N) returns the hypergeometric probability @.`HvS
density function at X with integer parameters M, K, and N. _ J"J [$
Note: The density function is zero unless X is an integer. QiRx2Z*\
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The size of Y is the common size of the input arguments. A scalar input yFFNzw{
functions as a constant matrix of the same size as the other inputs. ih:%U
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See also hygecdf, hygeinv, hygernd, hygestat, pdf. vl%Pg !l
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Reference page in Help browser ={ 190=\9
doc hygepdf MD> E0p)
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超几何分布参数较多，这里关于三个参数的指代不详。又在互联网上查了相关资料，包括该函数的定义式： !a5e{QG0
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http://ccpublic-1.central.cranfield.ac.uk/2001DMSOMFRC/pr062320/Matlab/stats/hygepdf.m W`wT0kP?*]
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直到发现这个例子后才清楚各个参数所代表的具体意义。 kwt;pxp i
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Suppose you have a lot of 100 floppy disks and you know that 20 of them are defective. What is the probability of drawing 0 through 5 defective floppy disks if you select 10 at random? L #IY6t
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p = hygepdf(0:5,100,20,10) 63i&e/pv
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p = 0.0951 0.2679 0.3182 0.2092 0.0841 0.0215 z5[Qh<M
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详细可参见： 3URrK[%x`
http://www.physnet.uni-hamburg.de/physnet/matlab/help/toolbox/stats/hygepdf.html#4257 U.W Mu%
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果然与一般对超几何分布公式字母惯常表示方式有所不同。尝试将上述分布作图如下 ux7g%Q ^"
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x = 0:5 <jVk}gi)Jp
p = hygepdf(x,100,20,10); o`ODz[ 04
plot(x,p,':k*')
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