1.4.40 ran: Generate a Random Number Between 0 and 1

Repeated calls to ran generate a sequence of random numbers with a uniform distribution. See lcrans(3m).

Example: ran:

demo% cat ran1.f
* ran1.f -- Generate random numbers.
       INTEGER*4 i, n
       real r(10)
       i = 760013
       do n = 1, 10
        r(n) = ran ( i )
       end do
       write ( *, "( 5 f11.6 )" ) r
       end
demo% f95 ran1.f
demo% a.out
   0.222058 0.299851 0.390777 0.607055 0.653188
   0.060174 0.149466 0.444353 0.002982 0.976519
demo%
 

Note the following:

• The range includes 0.0 and excludes 1.0.

• The algorithm is a multiplicative, congruential type, general random number generator.

• In general, the value of i is set once during execution of the calling program.

• The initial value of i should be a large odd integer.

• Each call to RAN gets the next random number in the sequence.

• To get a different sequence of random numbers each time you run the program, you must set the argument to a different initial value for each run.

• The argument is used by RAN to store a value for the calculation of the next random number according to the following algorithm:

    SEED = 6909 * SEED + 1 (MOD 2**32)

• SEED contains a 32-bit number, and the high-order 24 bits are converted to floating point, and that value is returned.