IMSL_RANDOM_TABLE

The IMSL_RANDOM_TABLE procedure sets or retrieves the current table used in either the shuffled or GFSR random number generator.

Note
This routine requires an IDL Advanced Math and Stats license. For more information, contact your ITT Visual Information Solutions sales or technical support representative.

Syntax

IMSL_RANDOM_TABLE, table [, /DOUBLE] [, /GET | /SET] [, /GFSR]

Arguments

table

One dimensional array used in the generators. For the shuffled generators table is length 128. For the GFSR generator table is length 1565. The argument table is input if the keyword Set is used, and output if the keyword Get is used.

Keywords

DOUBLE

If present and nonzero, double precision is used. This keyword is active only when the shuffled table is being set or retrieved.

GET

If present and nonzero, then the specified table is being retieved.

GFSR

If present and nonzero, then the specified GFSR table is being set or retrieved.

SET

If present and nonzero, then the specified table is being set.

Discussion

The values in table are initialized by the IMSL random number generators. The values are all positive except if you wish to reinitialize the array, in which case the first element of the array is input as a nonpositive value. (Usually, one should avoid reinitializing these arrays, but it might be necessary sometimes in restarting a simulation.) If the first element of table is set to a nonpositive value on the call to IMSL_RANDOM_TABLE with the keyword Set, on the next invocation of a routine to generate random numbers, the appropriate table will be reinitialized.

For more details on the shuffled and GFSR generators see the Overview: Random Number Generation.

Example

In this example, three separate simulation streams are used, each with a different form of the generator. Each stream is stopped and restarted. (Although this example is obviously an artificial one, there may be reasons for maintaining separate streams and stopping and restarting them because of the nature of the usage of the random numbers coming from the separate streams.)

nr = 5                           
iseed1 = 123457                  
iseed2 = 123457                  
iseed7 = 123457                  
 
; Begin first stream, iopt = 1 (by default)  
IMSL_RANDOMOPT,  Set = iseed1 
r = IMSL_RANDOM(nr) 
IMSL_RANDOMOPT,  Get = iseed1 
PM, r, TITLE = 'First stream output' 
 
First stream output 
   0.966220 
   0.260711 
   0.766262 
   0.569337 
   0.844829 
 
PRINT, 'output seed ', iseed1 
 
output seed   1814256879 
 
; Begin second stream, iopt = 2  
IMSL_RANDOMOPT,  gen_opt = 2 
IMSL_RANDOMOPT,  Set = iseed2 
r = IMSL_RANDOM(nr) 
IMSL_RANDOMOPT,  Get = iseed2 
IMSL_RANDOM_TABLE, table, /Get 
PM, r, TITLE = 'Second stream output' 
 
Second stream output 
   0.709518 
   0.186145 
   0.479442 
   0.603839 
   0.379015 
 
PRINT, 'output seed ', iseed2 
 
output seed   1965912801 
 
; Begin third stream, iopt = 7  
IMSL_RANDOMOPT,  gen_opt = 7 
IMSL_RANDOMOPT,  Set = iseed7 
r = IMSL_RANDOM(nr) 
IMSL_RANDOMOPT,  Get = iseed7 
IMSL_RANDOM_TABLE, itable, /Get, /GFSR 
PM, r, TITLE = 'Third stream output' 
 
Third stream output 
   0.391352 
   0.0262676 
   0.762180 
   0.0280987 
   0.899731 
 
PRINT, 'output seed ', iseed7 
 
output seed   1932158269 
 
; Reinitialize seed and resume first stream  
IMSL_RANDOMOPT,  gen_opt = 1 
IMSL_RANDOMOPT,  Set = iseed1 
r = IMSL_RANDOM(nr) 
IMSL_RANDOMOPT,  Get = iseed1 
PM, r, TITLE = 'First stream output' 
 
First stream output 
   0.0442665 
   0.987184 
   0.601350 
   0.896375 
   0.380854 
 
PRINT, 'output seed ', iseed1 
 
output seed    817878095 
 
; Reinitialize seed & table for shuffling & resume second stream  
IMSL_RANDOMOPT,  gen_opt = 2 
IMSL_RANDOMOPT,  Set = iseed2 
IMSL_RANDOM_TABLE, table, /Set 
r = IMSL_RANDOM(nr) 
IMSL_RANDOMOPT,  Get = iseed2 
PM, r, TITLE = 'Second stream output' 
 
Second stream output 
   0.255690 
   0.478770 
   0.225802 
   0.345467 
   0.581051 
 
PRINT, 'output seed ', iseed2 
 
output seed   2108806573 
 
; Reinitialize seed and table for GFSR and resume third stream. 
IMSL_RANDOMOPT,  GEN_OPT = 7 
IMSL_RANDOMOPT,  SET = iseed7 
IMSL_RANDOM_TABLE, itable, /SET, /GFSR 
r = IMSL_RANDOM(nr) 
IMSL_RANDOMOPT,  GET = iseed7 
PM, r, TITLE = 'Third stream output' 
 
Third stream output 
   0.751854 
   0.508370 
   0.906986 
   0.0910035 
   0.691663 
 
PRINT, 'output seed ', iseed7 
 
output seed   1485334679

Version History


6.4	Introduced