st: Random start to random number sequence

["Allan Reese (Cefas)" <allan.reese@cefas.co.uk>]

I looked on Statalist for a simple function to start the random number
generator with a random value and found lots of rather confusing
messages.  The Manual stresses the ability to repeat sequences from one
session to another, rather than to generate an (almost certainly for
practical purposes) unique sequence.  

The uniform() function to generate (pseudo) random numbers starts from
the same value in each Stata session unless you change the start value
with "set seed -value-", where value is an integer ([D] gen).  This is
very useful in allowing simulations to be repeatable but open to
variation: you get very different random sequences by setting the seed
to 1, 2, 3, etc.

On the other hand, you may simply require a different random sequence in
each session.  Rather than remember the seed values you have used
previously, you can use the system clock which changes every second.
This will not make the subsequent sequence any more (or less) random,
but will make each session unique.  The "code" (see -help seed- to
explain) can be displayed or saved in case you do want to reproduce a
session.

Using the clock has been suggested several time but with a complex
parsing.  Here is a simple program that can be added to your ado
library:

program define randomseed
   version 7
   local seed = clock( c(current_time), "hms" )
   set seed  `seed'
   di "Clock based seed = " c(seed)
end     


R Allan Reese
Senior statistician, Cefas
The Nothe, Weymouth DT4 8UB 

Tel: +44 (0)1305 206614 -direct
Fax: +44 (0)1305 206601 

www.cefas.co.uk 


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