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DRANDHYPERGEOMETRICREFERENCE / SRANDHYPERGEOMETRICREFERENCE

Initializes a reference vector for use with DRANDGENERALDISCRETE. Reference vector is for a Hypergeometric distribution with probability, f(X), defined by: f(X) = [s! * m! * (p - s)!] / [X! * (s - X)! * (m - X)! * (p - m - s + X)! * p!], if X = max(0,m+s-p),...,min(l,m), otherwise f(X) = 0. Here p is the size of the population, (NP), s is the size of the sample taken from the population, (NS) and m is the number of labeled, or specified, items in the population, (M).

(Note that SRANDHYPERGEOMETRICREFERENCE is the single precision version of DRANDHYPERGEOMETRICREFERENCE. The argument lists of both routines are identical except that any double precision arguments of DRANDHYPERGEOMETRICREFERENCE are replaced in SRANDHYPERGEOMETRICREFERENCE by single precision arguments - type REAL in FORTRAN or type float in C).

— SUBROUTINE: DRANDHYPERGEOMETRICREFERENCE (NP,NS,M,REF,LREF,INFO)
— Input: INTEGER NP

On input: size of population.
Constraint: NP>=0.

— Input: INTEGER NS

On input: size of sample being taken from population.
Constraint: 0<=NS <=NP.

— Input: INTEGER M

On input: number of specified items in the population.
Constraint: 0<=M <=NP.

— Output: DOUBLE PRECISION REF(LREF)

On output: if INFO returns with a value of 0 then REF contains reference information required to generate values from a Hypergeometric distribution using DRANDGENERALDISCRETE.

— Input/Output: INTEGER LREF

On input: either the length of the reference vector REF, or -1.
On output: if LREF=-1 on input, then LREF is set to the recommended length of the reference vector and the routine returns. Otherwise LREF is left unchanged.

— Output: INTEGER INFO

On output: INFO is an error indicator. If INFO = -i on exit, the i-th argument had an illegal value. If INFO =1 on exit, then LREF has been set to the recommended length for the reference vector REF. If INFO = 0 then the reference vector, REF, has been successfully initialized. 

     Example:
     

     
          C      Generate 100 values from the Hypergeometric distribution
                 INTEGER LSTATE,N
                 PARAMETER (LSTATE=16,N=100)
                 INTEGER I,INFO,SEED(1),STATE(LSTATE)
                 INTEGER NP, NS,M
                 INTEGER X(N)
                 INTEGER LREF
                 DOUBLE PRECISION REF(1000)
          
          C      Set the seed
                 SEED(1) = 1234
          
          C      Read in the distributional parameters
                 READ(5,*) NP, NS,M
          
          C      Initialize the STATE vector
                 CALL DRANDINITIALIZE(1,1,SEED,1,STATE,LSTATE,INFO)
          
          C      Initialize the reference vector
                 LREF = 1000
                 CALL DRANDHYPERGEOMETRICREFERENCE(NP, NS,M,REF,LREF,INFO)
          
          C      Generate N variates from the Hypergeometric distribution
                 CALL DRANDGENERALDISCRETE(N,REF,STATE,X,INFO)
          C      Print the results
                 WRITE(6,*) (X(I),I=1,N)