Scaling random numbers in Fortran

The Fortran rand() always returns a number between 0 and 1. More specifically, it is a number in the half-open interval [0,1), so you might get a 0.0 result, but the result will never be exactly 1.0 or greater.

Such a number can be scaled to produce uniformly distributed pseudorandom numbers in any interval.

• If you want an integer between i and j inclusive, use the expression:

          int(rand(0)*(j+1-i))+i

  For example, to get integers from 1 to 4, use:

          int(rand(0)*4)+1

• If you want a real number in the interval [x,y), use this expression:

          (rand(0)*(y-x))+x

  For example, to get numbers in the range [10,20), use:

          (rand(0)*10.0)+10.0

Last updated: 1995/12/19 18:58:09 UT
URL: http://www.nmt.edu/tcc/help/lang/fortran/scaling.html