;+ ; NAME: ; RAN2 ; ; PURPOSE: ; The RAN2 function returns one or more uniformly- ; distributed, floating-point, pseudo-random numbers in the ; range 0 LE Y < 1.0. ; ; The random number generator is taken from: "Numerical Recipes in C" ; 2nd Edition. It is long period (>2 x 10^18) random number ; generator of L'Ecuyer with Bays-Durham shuffle and added safeguards. ; Call with Seed a NEGATIVE OR UNDEFINED NUMBER TO INITIALIZE; ; thereafter, do not alter Seed between successive deviates in a sequence. ; ; CATEGORY: ; Math. ; ; CALLING SEQUENCE: ; ; Result = RAN2(Seed [, D1, ..., Dn]) ; ; INPUTS: ; Seed: A named variable containing the seed value for ; random number generation. Seed is updated by RAN2 ; once for each random number generated. The initial ; value of Seed should be set to different NEGATIVE values in ; order to obtain different random sequences. If Seed ; is undefined, it is derived from the system clock and ; is treated as an initial value. ; ; OPTIONAL INPUTS: ; Di: The dimensions of the result. The dimension ; parameters can be any scalar expression. Up to eight ; dimensions can be specified. If no dimensions are ; specified, RAN2 returns a scalar result ; ; OUTPUTS: ; This function returns uniform random deviates between 0.0 and 1.0 ; (exclusive of the endpoint values) with array dimensions given ; by the input parameters, D1, ..., Dn. ; ; RESTRICTIONS: ; Currently only available on the AIX platform. ; ; PROCEDURE: ; This function uses CALL_EXTERNAL to call an external sharable ; C object (ran2_.lib). This was done because coding the routine ; entirely in IDL would resulted in an unacceptably slow algorithm ; due to unavoidable for loops. ; ; MODIFICATION HISTORY: ; Written by: Han Wen, March 1996. ;- function RAN2, Seed, D1, D2, D3, D4, D5, D6, D7, D8 NP = N_PARAMS() case NP of 1 : r=0.0 2 : r=FLTARR(D1) 3 : r=FLTARR(D1,D2) 4 : r=FLTARR(D1,D2,D3) 5 : r=FLTARR(D1,D2,D3,D4) 6 : r=FLTARR(D1,D2,D3,D4,D5) 7 : r=FLTARR(D1,D2,D3,D4,D5,D6) 8 : r=FLTARR(D1,D2,D3,D4,D5,D6,D7) 9 : r=FLTARR(D1,D2,D3,D4,D5,D6,D7,D8) else : message,'Must have 1-9 parameters, '+\$ 'Seed [, D1,... D8]' endcase Ds = long(N_ELEMENTS(r)) if (N_ELEMENTS(Seed) eq 0) then Seed= -long(SYSTIME(1)) Seed= long(Seed) junk = CALL_EXTERNAL(GRPKPATH()+'ran2_.lib', 'ran2_', \$ Seed,Ds,r, /F_VALUE) return,r end