For users of SimPy, a discrete event simulation package for Python ()

Shutdown criterion

Hello...

I have a question, it is possible to stop a simulation with other criteria different to SimTime? for example I have a simulation model of a flowshop system and I want to stop the simulation when reaching certain level of production.

Thanks!!

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Tim Fish | 13 Mar 01:19

Re: [ SPAM ] Shutdown criterion

Typically a simulation is terminated when endtime is reached but it can be stopped at any time by the command:

stopSimulation( )

Tim

From: simpy-users-bounces <at> lists.sourceforge.net [mailto:simpy-users-bounces <at> lists.sourceforge.net] On Behalf Of Yennifer Santiago
Sent: 12 March 2008 23:52
To: simpy-users <at> lists.sourceforge.net
Subject: [ SPAM ] [Simpy-users] Shutdown criterion

Hello...

I have a question, it is possible to stop a simulation with other criteria different to SimTime? for example I have a simulation model of a flowshop system and I want to stop the simulation when reaching certain level of production.

Thanks!!

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Tony Vignaux | 13 Mar 02:25

REMOVE the prior argument from activate

I propose that the prior argument be removed from the activate and reactivate functions and the start method.

The command has the following syntax:

activate(p, p.pemname([args])[,{at=now()|delay=0}][,prior=False])

Setting prior = True allows one to ensure that a process object (entity) is given priority over other objects activated at the same time.

I suggest this is of little use, I have not heard of anyone using it, and I believe it makes maintaining the ordering of the event list more complicated. I can think of a number of methods of obtaining the same effect so why should we retain it? SimPy syntax is already too cluttered and we should work to simplify it.

Does anyone actually use this? Would anybody object if Klaus removed it?

Tony Vignaux

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kgmuller | 13 Mar 08:14

Re: Shutdown criterion

Very few models actually end at simulation endtime. That time is just a maximum value, but any condition can end a simulation before.

If you want to have a specific termination condition, you can use an observer process which does a "yield waituntil", followed by a call to stopSimulation.

Klaus Muller

From: simpy-users-bounces <at> lists.sourceforge.net [mailto:simpy-users-bounces <at> lists.sourceforge.net] On Behalf Of Yennifer Santiago
Sent: Thursday, March 13, 2008 12:52 AM
To: simpy-users <at> lists.sourceforge.net
Subject: [Simpy-users] Shutdown criterion

Hello...

I have a question, it is possible to stop a simulation with other criteria different to SimTime? for example I have a simulation model of a flowshop system and I want to stop the simulation when reaching certain level of production.

Thanks!!

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kgmuller | 14 Mar 09:23

Re: REMOVE the prior argument from activate

I support Tony's proposal, although I am the one who put the "prior" clause into activate. It comes from Simula, my model for the SimPy API.

What is wrong with "prior" is its semantics: what does it mean (in modelling terms) to put an event notice ahead of all event notices at the same time? What is the ordering of truly simultaneous events?

If one wishes to model one process to be executed before another process, one should model this explicitly by putting these processes into a priority queue.

Klaus Muller

From: simpy-users-bounces <at> lists.sourceforge.net [mailto:simpy-users-bounces <at> lists.sourceforge.net] On Behalf Of Tony Vignaux
Sent: Thursday, March 13, 2008 2:25 AM
To: SimPy Users
Subject: [Simpy-users] REMOVE the prior argument from activate

I propose that the prior argument be removed from the activate and reactivate functions and the start method.

The command has the following syntax:

activate(p, p.pemname([args])[,{at=now()|delay=0}][,prior=False])

Setting prior = True allows one to ensure that a process object (entity) is given priority over other objects activated at the same time.

I suggest this is of little use, I have not heard of anyone using it, and I believe it makes maintaining the ordering of the event list more complicated. I can think of a number of methods of obtaining the same effect so why should we retain it? SimPy syntax is already too cluttered and we should work to simplify it.

Does anyone actually use this? Would anybody object if Klaus removed it?

Tony Vignaux

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kgmuller | 17 Mar 14:37

Announcement of SimPy 1.9.1 bug-fix release

We announce the publication of SimPy 1.9.1, a bug-fix release of SimPy
version 1.9. Get it from
https://sourceforge.net/project/showfiles.php?group_id=62366 . If you are
using SimPy 1.9, this is a must-have release!

SimPy 1.9.1 cures two bugs:

(1) Excessive memory requirements of large or long-running scripts. This
performance problem was caused by circular references between Process and
event notice instances.

(2) Runtime errors for pre-empts of processes holding multiple Resource
objects.

Both problems were identified and reported by members of the SimPy user
community. Thanks for this, folks! Collaboration clearly pays off!

In addition to all other documentation, SimPy 1.9.1 provides a short manual
which only addresses the basic facilities of SimPy. You could consider this
as "SimPy light". This manual is aimed at introducing SimPy to beginners.
Tony is still developing this manual further. Your feedback is sought!

Tony Vignaux  Klaus Müller

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Shyamsundar, Purkayastha (Purkayastha)** CTR ** | 31 Mar 10:45

Modelling a communication link using SimPy resource facilities

Hi All

I need some suggestions about designing a LAN/WAN communication link using the SimPy resource facilities.

My basic requirements are that it should support some max bandwidth ( say 2 Mbps ) and it should connect two endpoints which will pump or retrieve data from it.

I have thought about it in the following ways.

- The Link will be implemented as a class which will essentially have two level resources and a temporary buffer.

- The two Level resources each having a capacity of 2048 and the unit is kbps. We need two levels for the Tx and the Rx direction of the link.

- A host which wants to pump data into the link acquires certain amount from the level and if it gets the amount then it places some data ( equivalent to the data in kbps ) in a temp buffer.

- The link class will pass the contents of the temp buffer to the other host on the receiving side and will replenish the level resource ( with the equivalent quantity of data transferred ) .

Same implementation will also apply to the other level resource as well for the host at the other end which wants to send some data.

My only worry is how to take care of the timing. Since this is a communication link which provides a resource only for certain time ( i.e 2048 kbps of data for 1 second ) , how do I ensure that the above steps ( for pumping and retrieving the data from the link ) are performed by ensuring the limits of 1 second ( or multiple of a second depending on the simulation time ) and the Link class implementation should ensure that at the beginning of a second, the level resource should have the maximum ( 2048 kbps ) capacity.

Any Suggestions ?

Thanks
Shyam.

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