[gmx-users] random number generation

[Jim Dix]

  To answer my own question: Gromacs uses a uniformly-distributed     
random number generator with a period of 10^8. The random numbers so  
generated are transformed into a Gaussian-distributed random numbers. 
Thus, if I figure correctly, on a 1000 atom BD simulation with a      
random force on each of the three dimensions, there would be at most 3
x 10^4 steps available before the "random" numbers repeated           
themselves. The lore is that one should not use a random number       
generator for more than 10-20% of its period, so that means that there
would be on the order of only 5000-10,000 BD steps available for a    
given seed to the random number generator. (?)                        
  Whether the random numbers generated by a particular seed are good  
random numbers still needs to be tested.                              
                                                                      
At 01:44 PM 2/28/03, you wrote:                                       
  I am doing a many-step Brownian dynamics simulation on a collection 
of small particles. Does anyone know how the pseudo-random numbers are
generated for Brownian random displacements? In particular, what is   
the period of the generator, and has it been shown to have no         
long-term spurious correlations?                                      
                                                                      
James A. Dix               |                                          
Associate Professor        | dix at binghamton.edu                       
Chemistry, Box 6016, SUNY  | voice: 607-777-2480                      
Vestal Parkway East        | fax: 607-777-2480                        
Binghamton, NY  13902-6016 |                                          
                                                                      
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James A. Dix               |                                          
Associate Professor        | dix at binghamton.edu                       
Chemistry, Box 6016, SUNY  | voice: 607-777-2480                      
Vestal Parkway East        | fax: 607-777-2480                        
Binghamton, NY  13902-6016 |