Functions and CALL Routines

CALL RANEXP Routine

Returns a random variate from an exponential distribution.

Category:

Random Number

Syntax
Arguments
Details
Comparisons
Examples
See Also

Syntax

CALL RANEXP(seed,x);

Arguments

seed

is the seed value. A new value for seed is returned each time CALL RANEXP is executed.

Range:	seed < 2³¹ - 1
Note:	If seed 0, the time of day is used to initialize the seed stream.
See:	Seed Values and Comparison of Seed Values in Random-Number Functions and CALL Routines for more information about seed values

x

is a numeric variable. A new value for the random variate x is returned each time CALL RANEXP is executed.

Details

The CALL RANEXP routine updates seed and returns a variate x that is generated from an exponential distribution that has a parameter of 1.

By adjusting the seeds, you can force streams of variates to agree or disagree for some or all of the observations in the same, or in subsequent, DATA steps.

The CALL RANEXP routine uses an inverse transform method applied to a RANUNI uniform variate.

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 RANEXP routine gives greater control of the seed and random number streams than does the RANEXP function.

Examples

This example uses the CALL RANEXP routine:

options pageno=1 ls=80 ps=64 nodate;

data u1(keep=x);
   seed = 104;
   do i = 1 to 5;
      call ranexp(seed, x); 
      output;
   end;
   call symputx('seed', seed);
run;

data u2(keep=x);
   seed = &seed;
   do i = 1 to 5;
      call ranexp(seed, x); 
      output;
   end;
run;

data all;
   set u1 u2;
   z = ranexp(104);
run;

proc print label;
   label x = 'Separate Streams' z = 'Single Stream';
run;

Output from the CALL RANEXP Routine

                                 The SAS System                                1

                                  Separate     Single
                           Obs     Streams     Stream

                             1     1.44347    1.44347
                             2     0.11740    0.11740
                             3     0.54175    0.54175
                             4     0.02280    0.02280
                             5     0.16645    0.16645
                             6     0.21711    0.21711
                             7     0.75538    0.75538
                             8     1.21760    1.21760
                             9     1.72273    1.72273
                            10     0.08021    0.08021