Hi Marek,
It would take a bit of poking, but it could be that the real problem is
setting the seed to 0, and if you use < 0, then the math in the Marsaglia
rng works out okay; I just have not checked it out and really only recently
noticed that there are no input range controls on ig in pmemd (probably
because there were none in sander). The reason that sander has the -1
feature and pmemd doesn't is that no one told me this was being done in
sander; I can miss new stuff that affects compatibility very easily unless
there is a specific test, because there is a huge volume of other irrelevant
changes as a general rule. Sorry for any trouble caused by this.
- Bob
----- Original Message -----
From: "Marek Maly" <marek.maly.ujep.cz>
To: "AMBER Mailing List" <amber.ambermd.org>
Sent: Thursday, June 04, 2009 12:35 PM
Subject: Re: [AMBER] use of random seed in multiple runs
Hi Bob,
I just finished some series of calculations and I have some another in
progress with setting ig=-1.
Of course that I really didn't assume that this complementary thermostat
setting is defined only for SANDER and not for PMEMD so
I used it also for the production PMEMD runs (using Amber10).
I had no time to do detail analysis yet but after reading of this
contribution I at least checked the temperature evolution
and it seems that it is OK (I used Langevin thermostat). I also checked
visually one of my simulated system and didn't
see any significant problems.
I have some another simulations with this setting (ig=-1) in progress so
it is question if it is not worth to
change ig setting there, but I would like to have all the simulations
done with the same setting ...
So please when you learn more about possible problems with this setting in
actual version of PMEMD, let me know
since I need to know if my results are trustable or not. As I already
mentioned, temperature control seems OK
but there could be another issues ...
Anyway if some serious "hazards" regarding to this setting in PMEMD will
be found, would be resonable to
notice in Amber users manual ( for example in this section: "2.6.8.
Temperature regulation" ), that
setting "ig=-1" is not implemented in the actual version of PMEMD and that
it is not recommended
sice it could cause some serious problems...
Thank you in advance for any additional info to this topic.
Best
Marek
Dne Thu, 04 Jun 2009 16:31:32 +0200 Robert Duke <rduke.email.unc.edu>
napsal/-a:
> Well, I would not recommend doing that. It looks to me like there is
> nothing to stop one from doing this in the code, but the random number
> initialization code clearly states the seed should be > 0. I would have
> to dink with it to see what really happens when you do this. The fix to
> actually use -1 is pretty simple; I can probably send out a patch at some
> point, or some simple directions for folks to hack their own code.
>
> Well, try this:
>
> In mdin_ctrl_dat.fpp, in the subroutine init_mdin_ctrl_dat(),
>
> In the variable declarations, change
>
> integer ifind
>
> to
>
> integer ifind, sec_temp
>
> Right before the "return" in the subroutine init_mdin_ctrl_dat() add the
> line:
>
> if (ig .eq. -1) call get_wall_time(sec_temp, ig)
>
>
> That's it. Really simple, very informal patch.
>
> - Bob
>
> ----- Original Message ----- From: "Jifeng Wang" <wangjf.gmail.com>
> To: "AMBER Mailing List" <amber.ambermd.org>
> Sent: Thursday, June 04, 2009 10:10 AM
> Subject: Re: [AMBER] use of random seed in multiple runs
>
>
>> On Wed, Jun 3, 2009 at 11:59 PM, Robert Duke <rduke.email.unc.edu>
>> wrote:
>>
>>> Note that the -1 capability is not yet in a released version of pmemd
>>> (I
>>> think we have it in the pmemd 11 codebase).
>>> - Bob
>>>
>>
>> Is it ok to use "-1" itself as a random seed for PMEMD?
>>
>>
>>>
>>> ----- Original Message ----- From: "Gustavo Seabra" <
>>> gustavo.seabra.gmail.com>
>>> To: "AMBER Mailing List" <amber.ambermd.org>
>>> Sent: Wednesday, June 03, 2009 10:00 PM
>>> Subject: Re: [AMBER] use of random seed in multiple runs
>>>
>>>
>>>
>>> Any group of simulations using stochastic thermostats, including
>>> Langevin, is subject to synchronization effects if using the same seed
>>> for all simulations, and eventually you end up with all correlated
>>> runs, which influences your statistics. Note that, in Amber10, you can
>>> avoid that by just using 'ig=-1' in all cases. That will tell sander
>>> to generate a new random seed every time, I believe based on clock
>>> time.
>>>
>>> Gustavo Seabra
>>> Postdoctoral Associate
>>> Quantum Theory Project - University of Florida
>>> Gainesville - Florida - USA
>>>
>>> -------------------------------------------------------------------------------------------
>>> Q: Why do mountain climbers rope themselves together?
>>> A: To prevent the sensible ones from going home.
>>>
>>>
>>>
>>>
>>> On Wed, Jun 3, 2009 at 3:26 PM, Andrew Voronkov <drugdesign.yandex.ru>
>>> wrote:
>>>
>>>> Only that I did several runs in this way...ok so I'll remake it.
>>>>
>>>> 03.06.09, 17:55, "Gustavo Seabra" <gustavo.seabra.gmail.com>:
>>>>
>>>> Do you have any reason *not* tuo use a differend random seed for each
>>>>> run?
>>>>> Gustavo Seabra
>>>>> Postdoctoral Associate
>>>>> Quantum Theory Project - University of Florida
>>>>> Gainesville - Florida - USA
>>>>>
>>>>> -------------------------------------------------------------------------------------------
>>>>> Q: Why do mountain climbers rope themselves together?
>>>>> A: To prevent the sensible ones from going home.
>>>>> On Wed, Jun 3, 2009 at 5:28 AM, Andrew Voronkov
>>>>> <drugdesign.yandex.ru>
>>>>> wrote:
>>>>> > I want to make 30-50 nanosecond run of the protein with explicit >
>>>>> waters. But I have limitations on our cluster for time of each job.
>>>>> Can > I
>>>>> divide it in several (let's say 5-10 nanosecond runs) without random
>>>>> > seed
>>>>> or I need to use random seed in each restart? (output rst -> input >
>>>>> rst).
>>>>> Main question of the study is to look at stability of the > structure
>>>>> and
>>>>> make average structure from stability parts of > trajectpry.
>>>>> >
>>>>> > Best regards,
>>>>> > Andrew Voronkov
>>>>> >
>>>>> > _______________________________________________
>>>>> > AMBER mailing list
>>>>> > AMBER.ambermd.org
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Received on Fri Jun 05 2009 - 01:11:11 PDT
