RNUNF

This function generates a pseudorandom number from a uniform (0, 1) distribution.

Function Return Value

RNUNF — Function value, a random uniform (0, 1) deviate. (Output)
See Comment 1.

Required Arguments

None.

FORTRAN 90 Interface

Generic: RNUNF()

Specific: The specific interface names are S_RNUNF and D_RNUNF.

FORTRAN 77 Interface

Single: RNUNF()

Double: The double precision name is DRNUNF.

Description

Routine RNUNF is the function form of RNUN. The routine RNUNF generates pseudorandom numbers from a uniform (0, 1) distribution. The algorithm used is determined by RNOPT. The values returned by RNUNF are positive and less than 1.0.

If several uniform deviates are needed, it may be more efficient to obtain them all at once by a call to RNUN rather than by several references to RNUNF.

Comments

1. If the generic version of this function is used, the immediate result must be stored in a variable before use in an expression. For example:

X = RNUNF()
Y = SQRT(X)

must be used rather than

Y = SQRT(RNUNF())

If this is too much of a restriction on the programmer, then the specific name can be used without this restriction.

2. The routine RNSET can be used to initialize the seed of the random number generator. The routine RNOPT can be used to select the form of the generator.

3. This function has a side effect: it changes the value of the seed, which is passed through a common block.

Example

In this example, RNUNF is used to generate five pseudorandom uniform numbers. Since RNOPT is not called, the generator used is a simple multiplicative congruential one with a multiplier of 16807.

 

USE UMACH_INT

USE RNSET_INT

USE RNUNF_INT

 

IMPLICIT NONE

INTEGER I, ISEED, NOUT

REAL R(5)

!

CALL UMACH (2, NOUT)

ISEED = 123457

CALL RNSET (ISEED)

DO 10 I=1, 5

R(I) = RNUNF()

10 CONTINUE

WRITE (NOUT,99999) R

99999 FORMAT (' Uniform random deviates: ', 5F8.4)

END

Output

 

Uniform random deviates: 0.9662 0.2607 0.7663 0.5693 0.8448