1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
|
DOUBLE PRECISION FUNCTION DLARAN( ISEED )
*
* -- LAPACK auxiliary routine (version 3.0) --
* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
* Courant Institute, Argonne National Lab, and Rice University
* February 29, 1992
*
* .. Array Arguments ..
INTEGER ISEED( 4 )
* ..
*
* Purpose
* =======
*
* DLARAN returns a random real number from a uniform (0,1)
* distribution.
*
* Arguments
* =========
*
* ISEED (input/output) INTEGER array, dimension (4)
* On entry, the seed of the random number generator; the array
* elements must be between 0 and 4095, and ISEED(4) must be
* odd.
* On exit, the seed is updated.
*
* Further Details
* ===============
*
* This routine uses a multiplicative congruential method with modulus
* 2**48 and multiplier 33952834046453 (see G.S.Fishman,
* 'Multiplicative congruential random number generators with modulus
* 2**b: an exhaustive analysis for b = 32 and a partial analysis for
* b = 48', Math. Comp. 189, pp 331-344, 1990).
*
* 48-bit integers are stored in 4 integer array elements with 12 bits
* per element. Hence the routine is portable across machines with
* integers of 32 bits or more.
*
* =====================================================================
*
* .. Parameters ..
INTEGER M1, M2, M3, M4
PARAMETER ( M1 = 494, M2 = 322, M3 = 2508, M4 = 2549 )
DOUBLE PRECISION ONE
PARAMETER ( ONE = 1.0D+0 )
INTEGER IPW2
DOUBLE PRECISION R
PARAMETER ( IPW2 = 4096, R = ONE / IPW2 )
* ..
* .. Local Scalars ..
INTEGER IT1, IT2, IT3, IT4
* ..
* .. Intrinsic Functions ..
INTRINSIC DBLE, MOD
* ..
* .. Executable Statements ..
*
* multiply the seed by the multiplier modulo 2**48
*
IT4 = ISEED( 4 )*M4
IT3 = IT4 / IPW2
IT4 = IT4 - IPW2*IT3
IT3 = IT3 + ISEED( 3 )*M4 + ISEED( 4 )*M3
IT2 = IT3 / IPW2
IT3 = IT3 - IPW2*IT2
IT2 = IT2 + ISEED( 2 )*M4 + ISEED( 3 )*M3 + ISEED( 4 )*M2
IT1 = IT2 / IPW2
IT2 = IT2 - IPW2*IT1
IT1 = IT1 + ISEED( 1 )*M4 + ISEED( 2 )*M3 + ISEED( 3 )*M2 +
$ ISEED( 4 )*M1
IT1 = MOD( IT1, IPW2 )
*
* return updated seed
*
ISEED( 1 ) = IT1
ISEED( 2 ) = IT2
ISEED( 3 ) = IT3
ISEED( 4 ) = IT4
*
* convert 48-bit integer to a real number in the interval (0,1)
*
DLARAN = R*( DBLE( IT1 )+R*( DBLE( IT2 )+R*( DBLE( IT3 )+R*
$ ( DBLE( IT4 ) ) ) ) )
RETURN
*
* End of DLARAN
*
END
|
