1 |
C $Header: /u/u3/gcmpack/MITgcm/model/src/port_rand.F,v 1.3 2001/09/26 18:09:16 cnh Exp $ |
2 |
C $Name: $ |
3 |
|
4 |
C Portable random number generator |
5 |
|
6 |
#undef _USE_INTEGERS |
7 |
|
8 |
! ============================================================================== |
9 |
CBOP |
10 |
C !ROUTINE: port_rand |
11 |
C !INTERFACE: |
12 |
real*8 function port_rand(seed) |
13 |
|
14 |
C !DESCRIPTION: \bv |
15 |
C Portable random number generator |
16 |
C \ev |
17 |
|
18 |
C !LOCAL VARIABLES: |
19 |
implicit none |
20 |
integer nff |
21 |
parameter(nff=55) |
22 |
#ifdef _USE_INTEGERS |
23 |
integer mbig,mseed,mZ,seed |
24 |
#else |
25 |
real*8 mbig,mseed,mz,seed |
26 |
#endif |
27 |
real*8 fac |
28 |
#ifdef _USE_INTEGERS |
29 |
parameter (mbig=1000000000,mz=0,fac=1./mbig) |
30 |
data mseed/161803398/ |
31 |
#else |
32 |
parameter (mbig=4000000.,mz=0.,fac=1./mbig) |
33 |
data mseed/1618033./ |
34 |
#endif |
35 |
integer i,ii,inext,inextp,k,idum |
36 |
parameter(idum=-2) |
37 |
#ifdef _USE_INTEGERS |
38 |
integer mj,mk,ma(nff) |
39 |
#else |
40 |
real*8 mj,mk,ma(nff) |
41 |
#endif |
42 |
logical firstCall |
43 |
save firstCall,inext,inextp,ma |
44 |
data firstCall /.true./ |
45 |
CEOP |
46 |
! ------------------------------------------------------------------------------ |
47 |
mseed = seed |
48 |
if(firstCall)then |
49 |
firstCall=.false. |
50 |
mj=mseed-iabs(idum) |
51 |
mj=mod(mj,mbig) |
52 |
ma(nff)=mj |
53 |
mk=1 |
54 |
do i=1,nff-1 |
55 |
ii=mod(21*i,nff) |
56 |
ma(ii)=mk |
57 |
mk=mj-mk |
58 |
if(mk.lt.mz)mk=mk+mbig |
59 |
mj=ma(ii) |
60 |
enddo |
61 |
do k=1,4 |
62 |
do i=1,nff |
63 |
ma(i)=ma(i)-ma(1+mod(i+30,nff)) |
64 |
if(ma(i).lt.MZ)ma(i)=ma(i)+mbig |
65 |
enddo |
66 |
enddo |
67 |
inext=0 |
68 |
inextp=31 |
69 |
endif |
70 |
inext=mod(inext,nff)+1 |
71 |
inextp=mod(inextp,nff)+1 |
72 |
mj=ma(inext)-ma(inextp) |
73 |
if(mj.lt.MZ)mj=mj+mbig |
74 |
ma(inext)=mj |
75 |
port_rand=mj*fac |
76 |
return |
77 |
! ------------------------------------------------------------------------------ |
78 |
end |
79 |
! ============================================================================== |
80 |
|
81 |
! ============================================================================== |
82 |
subroutine port_ranarr(n,arr) |
83 |
implicit none |
84 |
integer n,i |
85 |
real arr(n) |
86 |
real*8 port_rand,seed |
87 |
seed=1618033.0d0 |
88 |
! ------------------------------------------------------------------------------ |
89 |
do i=1,n |
90 |
arr(i)=port_rand(seed) |
91 |
enddo |
92 |
|
93 |
return |
94 |
! ------------------------------------------------------------------------------ |
95 |
end |
96 |
! ============================================================================== |