random numbers on clusters

[Michael Creel]

David Bateman wrote:
> If your platform as /dev/urandom, then the octave-forge random 
> generators will use it to seed the generators, and you will end up with 
> independent number streams. Even if you don't have /dev/urandom, then 
> these generators use the LSB of the clock to seed with (ie. usec) and so 
> you'll probably find yourself with independent streams in any case.

Hi David and list,

Looking into this, I found the definition

"Least Significant Bit (LSB) The LSB is the right most bit in a binary number. 
For Example 00000001, 1 is the LSB."

>From rand.cc:
"By default, the generator is initialized from /dev/urandom if it is\n\
available,otherwise from cpu time, wall clock time and the current\n\
fraction of a second.\n\"

I'm guessing that LSB here means decimal rather than binary numbers, but if 
that's true then when the clock is used to initialize, then there are only 10 
possible starting points for the sequence of random numbers. (?) If this is 
the case then correlated streams on different nodes would be quite likely 
even if only a small number of nodes are used, and it would be a certaintly 
on any cluster with more than 10 nodes. I guess that this might be relevant 
on Windows machines.

Hoping I'm confused, Michael



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