ending a simulation

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Re: ending a simulation

Tim Condit wrote:
> Hi,
>
> I've wondered about something, but so far have not had time to look 
> more closely at it.  So I'm wondering if others have done something 
> like this before.
>
> I'm gathering statistics from a simulation of Taxis and Fares.  One of 
> them is the span of time from Fare activation, until pickup by a 
> Taxi.  The second is the span of time from when the Fare is picked up, 
> until it is dropped off at its destination.  In every simulation, I 
> wind up with three distinct groups of Fares: those that are picked up 
> and taken to their destination, essentially completing the Fare's 
> lifecycle; those that are picked up, but are still en'route when the 
> simulation ends; and those that never get picked up at all, for one 
> reason or another.
>
> The problem I have (or maybe only imagine I have) is that this 
> presents something of a dilemma when I'm trying to gather data with a 
> Monitor.  I'm not sure how to report it!  Whatever I do with it at 
> this point, it's a separate set (or sets) of data, that I'd like 
> incorporated into the data for completed Fares.  So I'm thinking about 
> using a sort of compound condition for terminating a simulation.  That 
> would leave me with just the completed Fares and the waiting Fares, 
> which is more manageable.  I tried this,
>
>     simulate(until=(SIMTIME and len(Agents.waitingFares.theBuffer) == 0))
>
> but it doesn't work, and I'm not sure why.  It almost seems to behave 
> like I'm using a logical OR instead of AND in there.  The simulation 
> starts up, and as the buffer is almost immediately emptied the 
> simulation terminates, even though it's nowhere near SIMTIME.  Now I'm 
> thinking about just calculating the time remaining for the en'route 
> Fares to reach their destinations, and adding those Fares to the set 
> of completed Fares, with a note to that effect.  But it's definitely a 
> second choice.
>
> Has anyone tried anything like this?  Had any success with it?  More 
> generally, does anyone have strategies or pointers to documentation 
> for dealing with these types of loose ends in data collection?

I believe that simulate expects a boolean argument, terminating when it 
evaluates to true.
Try something like:
simulate(until=((SimPy.Simulation.now() >= SIMTIME) and 
len(Agents.waitingFares.theBuffer) == 0))

# Steve

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SimPy Book

What's the status of the SimPy book?  Also, while looking at the sample 
chapter on the web site I question the assert statement following the line:

yield Sim.request,self,ban.manager

It doesn't seem needed for the example, though it would be useful for a 
SimPy unit test.

Regards,
Steve

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Re: ending a simulation

Thanks for the suggestion Steve.  Unfortunately, it terminates
prematurely in exactly the same way.

On 6/10/07, Steven H. Rogers <steve <at> shrogers.com> wrote:
> Tim Condit wrote:
> > Hi,
> >
> > I've wondered about something, but so far have not had time to look
> > more closely at it.  So I'm wondering if others have done something
> > like this before.
> >
> > I'm gathering statistics from a simulation of Taxis and Fares.  One of
> > them is the span of time from Fare activation, until pickup by a
> > Taxi.  The second is the span of time from when the Fare is picked up,
> > until it is dropped off at its destination.  In every simulation, I
> > wind up with three distinct groups of Fares: those that are picked up
> > and taken to their destination, essentially completing the Fare's
> > lifecycle; those that are picked up, but are still en'route when the
> > simulation ends; and those that never get picked up at all, for one
> > reason or another.
> >
> > The problem I have (or maybe only imagine I have) is that this
> > presents something of a dilemma when I'm trying to gather data with a
> > Monitor.  I'm not sure how to report it!  Whatever I do with it at
> > this point, it's a separate set (or sets) of data, that I'd like
> > incorporated into the data for completed Fares.  So I'm thinking about
> > using a sort of compound condition for terminating a simulation.  That
> > would leave me with just the completed Fares and the waiting Fares,
> > which is more manageable.  I tried this,
> >
> >     simulate(until=(SIMTIME and len(Agents.waitingFares.theBuffer) == 0))
> >
> > but it doesn't work, and I'm not sure why.  It almost seems to behave
> > like I'm using a logical OR instead of AND in there.  The simulation
> > starts up, and as the buffer is almost immediately emptied the
> > simulation terminates, even though it's nowhere near SIMTIME.  Now I'm
> > thinking about just calculating the time remaining for the en'route
> > Fares to reach their destinations, and adding those Fares to the set
> > of completed Fares, with a note to that effect.  But it's definitely a
> > second choice.
> >
> > Has anyone tried anything like this?  Had any success with it?  More
> > generally, does anyone have strategies or pointers to documentation
> > for dealing with these types of loose ends in data collection?
>
> I believe that simulate expects a boolean argument, terminating when it
> evaluates to true.
> Try something like:
> simulate(until=((SimPy.Simulation.now() >= SIMTIME) and
> len(Agents.waitingFares.theBuffer) == 0))
>
> # Steve
>
>
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> Simpy-users <at> lists.sourceforge.net
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Re: ending a simulation

Tim Condit wrote:
> Thanks for the suggestion Steve.  Unfortunately, it terminates
> prematurely in exactly the same way.
>
>   
Tim:

Sorry about that.  I looked at the Simulation.simulate code and it's 
expecting a number for until and defaults to 0.

Another thing to try is put a statement like this in your model() function.

If (SimPy.Simulation.now() >= SIMTIME) and len(Agents.waitingFares.theBuffer) == 0)):
    Simpy.Simulation.stopSimulation()

# Steve

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Re: ending a simulation

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Re: ending a simulation

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Re: ending a simulation

Tim Condit wrote:
> Sure, I can set the endtime later than when the last fare is created.  
> That's no problem.  I was looking for a solution that appealed to me 
> aesthetically, but it's not blocking me. :)
It would be nice to have another optional parameter, say until_condition 
which could be a boolean expression or variable for Simulation.simulate().

# Steve

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Re: ending a simulation

Steve,
Yes, this would be possible, but it would slow down the execution of SimPy,
as does any waiting for a general Boolean condition. If you want to
implement such terminating condition, you can use "yield waituntil" in
today's SimPy already.

Klaus Müller 

> -----Original Message-----
> From: Steven H. Rogers [mailto:steve <at> shrogers.com] 
> Sent: Wednesday, June 13, 2007 3:45 AM
> To: Tim Condit
> Cc: Klaus Muller; simpy-users
> Subject: Re: [Simpy-users] ending a simulation
> 
> Tim Condit wrote:
> > Sure, I can set the endtime later than when the last fare 
> is created.  
> > That's no problem.  I was looking for a solution that 
> appealed to me 
> > aesthetically, but it's not blocking me. :)
> It would be nice to have another optional parameter, say 
> until_condition which could be a boolean expression or 
> variable for Simulation.simulate().
> 
> # Steve
> 
> 

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Saving and restarting SimPy simulations

All:
Python's pickle/cpickle does not support pickling generators (a stupid
omission, considering the power of generators). Simply saving the state of a
SimPy simulation by pickling is therefore not possible.

As quite a number of you have indicated a requirement for saving and
restarting SimPy simulations, I have written up an article giving recipes
and examples for making SimPy simulations saveable and restartable. You find
it at the SimPy website http://SimPy.Sourceforge.net.

The article gives a workaround approach, based on removing generators at
saving and reinstating them at restarting. Obviously, some programming is
required.

If you think that this is unnecessary programming overhead (as I do), lean
on Python's developers and ask for pickle or cpickle to be changed to
support the pickling of generators. They should make generators first class
Python citizens!

Klaus Müller

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