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% f77 -silent 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.