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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 NOo&5@z;H
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ans = 2<YHo{0BLS
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查看了一下帮助 help hygepdf F;`es%8
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HYGEPDF Hypergeometric probability density function. 3^ wJ4=^
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Y = HYGEPDF(X,M,K,N) returns the hypergeometric probability 3-tp94`8}t
density function at X with integer parameters M, K, and N. l&5| =
Note: The density function is zero unless X is an integer. z_r W1?|
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The size of Y is the common size of the input arguments. A scalar input Zb8i[1 P
functions as a constant matrix of the same size as the other inputs. 21G] d
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See also hygecdf, hygeinv, hygernd, hygestat, pdf. ?=f\oH$
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Reference page in Help browser % %kl R{
doc hygepdf 6 3K ec
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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： Zna
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http://ccpublic-1.central.cranfield.ac.uk/2001DMSOMFRC/pr062320/Matlab/stats/hygepdf.m v]Pw]m5=U
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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。 cb|`)"<HN
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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? Cg8{NNeD
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p = hygepdf(0:5,100,20,10) ApjL Y58=
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p = 0.0951 0.2679 0.3182 0.2092 0.0841 0.0215 4hZ-^AL"(
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详细可参见： (47jop0RDQ
http://www.physnet.uni-hamburg.de/physnet/matlab/help/toolbox/stats/hygepdf.html#4257 0Rrz
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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 k $3.FO"
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x = 0:5 CA[k$Sw*
p = hygepdf(x,100,20,10); Pr @ EpO
plot(x,p,':k*')
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