FREE_R set

Phil Jeffrey phil at XRAY2.MSKCC.ORG
Thu Nov 12 16:38:05 EST 1998

On Thu, 12 Nov 1998, Hongmin Li wrote:

> I am curious about generating Free_R flag for reflection files. I found that
> when I used X-PLOR setup_free_r.inp to generate free set, it seemed that the
> 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 same.

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, |
| Memorial Sloan-Kettering Cancer Center, NYC   | it will get its revenge     |
| phil at                          |     - Henry Spencer         |
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