Functions and CALL Routines

RANTBL Function

Returns a random variate from a tabled probability distribution.

Category:	Random Number
Tip:	If you want to change the seed value during execution, you must use the CALL RANTBL routine instead of the RANTBL function.

Syntax
Arguments
Details
Comparisons
See Also

Syntax

RANTBL(seed,p1 ,... p_i... ,p_n)

Arguments

seed

is a numeric constant, variable, or expression with an integer value. If seed [le] 0, the time of day is used to initialize the seed stream.

Range:	seed < 2³¹-1
See:	Seed Values for more information about seed values

p_i

is a numeric constant, variable, or expression.

Range:

p_i

1 for 0 <i [le]

Details

The RANTBL function returns a variate that is generated from the probability mass function defined by p₁ through p_n . An inverse transform method applied to a RANUNI uniform variate is used. RANTBL returns

[equation]

If, for some index j<n, [equation] , RANTBL returns only the indices 1 through j with the probability of occurrence of the index j equal to .

Let n=3 and P1, P2, and P3 be three probabilities with P1+P2+P3=1, and M1, M2, and M3 be three variables. The variable X in these statements

array m{3} m1-m3;
x=m{rantbl(seed,of p1-p3)};

will be assigned one of the values of M1, M2, or M3 with probabilities of occurrence P1, P2, and P3, respectively.

For a discussion and example of an effective use of the random number CALL routines, see Starting, Stopping, and Restarting a Stream.

Comparisons

The CALL RANTBL routine, an alternative to the RANTBL function, gives greater control of the seed and random number streams.