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Annotation of 43BSDTahoe/new/help/src/f77/random, revision 1.1.1.1

1.1       root        1: .TI F77/RANDOM "Sep. 4, 1985"
                      2: Random Number Generators
                      3: 
                      4: You can generate sequences of random numbers using random()
                      5: from the f77 system library, or by using procedures in the IMSL or
                      6: NAG libraries.
                      7: This help file includes examples using random(),
                      8: ggubs() from the IMSL library and g05caf() from the NAG library.
                      9: ggubs() and g05caf() are recommended over random().
                     10: See "help f77 nag" and "help f77 imsl" for information on whether IMSL
                     11: and NAG are available on this system.
                     12: 
                     13: The functions random(), irandm(), and drandm() in the f77 library
                     14: provide sequence of real, integer and double precision random numbers.
                     15: To get a sequence of 100 pseudo-random numbers between 0 and 1.0:
                     16: 
                     17: .nf
                     18:                real x(100)
                     19:                   ...
                     20:                x(1) = random(1)
                     21:                do 10 i=2,100
                     22:        10      x(i) = random(0)
                     23: .fi
                     24: 
                     25: The first call with argument of 1 starts the sequence with the same
                     26: number each time the program is run.  This is useful for debugging when
                     27: you need to compare two runs.  The later calls with argument of 0
                     28: cause the next random number in the sequence to be returned.  If you
                     29: want to generate a different sequence each time the program is run,
                     30: use:
                     31: 
                     32: .nf
                     33:                integer time
                     34:                real x(100)
                     35:                   ...
                     36:                x(1) = random(time())
                     37:                do 10 i=2,100
                     38:        10      x(i) = random(0)
                     39: .fi
                     40: 
                     41: For details, see "man 3f random".
                     42: 
                     43: NAG section G05 and IMSL chapter G contain over 80 subroutines dealing
                     44: with generating and testing pseudo-random numbers.  To generate a
                     45: sequence of 100 single precision pseudo-random numbers in the interval (0.,1.)
                     46: using IMSL's ggubs:
                     47: 
                     48: .nf
                     49:              real randsp(100), ggubfs
                     50:              double precision dseed
                     51: 
                     52:              dseed = 123457.d0
                     53:              do 20 i = 1, 100
                     54:        20    randsp(i) =  ggubfs( dseed )
                     55: .fi
                     56: 
                     57: \&'dseed' is changed by ggubfs(), so it must be a variable and your program
                     58: must not change it between calls to ggubfs().  The sequence generated depends
                     59: on the initial value of 'dseed'; it must be between 1.0d0 and 2147483647.0d0 .
                     60: To access the IMSL library, add '-limsld' at the end of your f77 command.
                     61: 
                     62: To generate a sequence of 100 double pseudo-random precision numbers
                     63: in the interval (0.,1.) using NAG's g05caf():
                     64: 
                     65: .nf
                     66:              double precision randdp(100), g05caf
                     67: 
                     68:              do 30 i = 1,100
                     69:        30    randdp(i) = g05caf(dummy)
                     70: .fi
                     71: 
                     72: g05caf() uses common blocks /ag05ca/ and /bg05ca/, so your program
                     73: should not changes values in these common blocks.  This generates the
                     74: same sequence each time it is used; to generate a different sequence
                     75: each time your program is run, begin your program with:
                     76: 
                     77:              call g05ccf
                     78: 
                     79: g05ccf should be called before the first call on g05caf() and should be
                     80: called only once.  It will initialize the random sequence using the
                     81: current time to generate a seed.  To access the NAG library,
                     82: add '-lnagd' at the end of your f77 command.

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