FREE_R set

Bernhard Rupp br at LLNL.GOV
Thu Nov 12 18:43:19 EST 1998

There are standard FORTRAN routines to set the random
seed and then to get 'random' random numbers. 
Code below creates a random filename of letters.

      subroutine random_name (fname,fext,in,num)
      character fname*(*),fext*4 
      integer iran(in) 
      real rand(in)  
      call random_seed ()    
      call random_number (rand)  
      do i=1,in      
      end do              

Mfg, BR

At 04:41 PM 11/12/98 -0500, Phil Jeffrey wrote:
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>On Thu, 12 Nov 1998, Hongmin Li wrote:
>> I am curious about generating Free_R flag for reflection files. I found
>> when I used X-PLOR setup_free_r.inp to generate free set, it seemed that
>> freeflag assignment was not random. Because when I run the script
several times
>> for the same beginning reflection file, the generated free sets were the
>This is because "random" number generators on computers are not truly
>random, but approximate it.  If you give the Random Number Generator the
>same starting value each time (as X-PLOR probably does) then you'll get
>the same sequence of numbers out of it leading to the same freeR set.
>(Alternatives, such as seeding the generator from the integer value of the
>computer clock, are well-known, but probably beyond the scope of the
>user to implement in X-PLOR).
>| Phil Jeffrey                                  |
>| Crystallography Facility Manager              | If you lie to the
compiler, |
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Dr. Bernhard Rupp
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