Re: [Ngspice-devel] Thread in DCtran

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 Yash,
wrt. BE your comment is not absolute correct: You can use .option maxord=1 to switch trapez to BE.
(See also niiter.c.)
But not testet so much!

Dietmar

----- Original Nachricht ----
Von:     Yash Dosi <yas...@gm...>
An:      "Ngspice developers mailing list." <ngs...@li...>
Datum:   19.11.2012 08:13
Betreff: Re: [Ngspice-devel] Thread in DCtran

> Hey Francesco,
> Extremely sorry for the late reply. But I have terribly busy lately.
> But I believe our ngspice versions are different. I have ngspice-24.
> And in the end of DCtran.c there is no call to CKTerr routine.
> Also ngspice-24 does not have BE implementation also. It just has Trap &
> Gear.
> 
> Another thing after studying the data-dependency for the ckt structure I
> think creating another duplicate instance is the only solution. So I have
> started working in that direction.
> Please do correct me if I am wrong.
> 
> On Mon, Nov 5, 2012 at 6:40 PM, Francesco Lannutti
> <nic...@fa...>wrote:
> 
> > Hi Yash,
> > standing to the article they predict the next time point using FE method,
> > because it's explicit, but I have to say it's not accurate.
> > In SPICE and NGSPICE too, the time point is handled like this:
> > 1) At the end of DCtran.c you will find a call to CKTterr routine.
> > 2) This is a wrapper on the DEVtrunc routines that compute the local
> > truncation error performed by every model serially, calling the CKTtrunc
> > routine.
> > 3) This step adjusts the proposed time step.
> > 4) Goto next point.
> >
> > Without this check you cannot proceed along a verified time step path. In
> > the paper it seems they compute some time points assuming the correctness
> > of the prediction through FE. Only after that, they control the
> correctness
> > using one of inter-thread communication, that will require something like
> a
> > critical section or atomic routines.
> > IMHO this is not the correct way to proceed to have a huge parallelism.
> >
> > BTW, to achieve the same results you have to touch:
> > 1) The end part of the DCtran.c , changing the way to check the next time
> > step correctness ;
> > 2) The NIiter.c , in which the Newton-Raphson Cycle is coded, in order to
> > handle the inter-thread communication in the NR Cycle ;
> > 3) The NIinteg.c , in which the Integration Methods are coded, in order
> to
> > add the FE Method, because NGSPICE only has BE, Trapezoidal and Gear
> method.
> >
> > This as starting point.
> > Think about the option to start from the GIT master branch?
> >
> > Good luck with that ! :)
> >
> > Fra
> >
> >
> > Il giorno 05/nov/2012, alle ore 13:36, Yash Dosi <yas...@gm...> ha
> > scritto:
> >
> > Hi Francesco & Stefano,
> >     I don't think this is completely impossible.
> >     Some work related to parallelizing Gear Method is already done. Have
> a
> > look at this:
> >     http://dl.acm.org/citation.cfm?id=1391531
> >     For a start I can just try to implement this in ngspice.
> >
> > By the way, thanks for warning me about the cloning ckt.
> > Can this be done?
> > If yes how or some direction in which I can proceed?
> >
> > On Mon, Nov 5, 2012 at 5:05 PM, Francesco Lannutti
> <nic...@fa...
> > > wrote:
> >
> >> Hi Yash,
> >> summarizing your intent, you want to parallelize the execution of one
> >> integration method, let's say Gear or Trapezoidal. If so, I have to
> agree
> >> with Stefano, you cannot do that in my opinion, because you are trying
> to
> >> parallelize something that is intrinsically serial.
> >> However, the integration method is calculated by NIintegrate under
> >> src/maths/ni and it uses some state vector, depending on how many time
> >> points in the past you want to track (DCtran uses at the most 4 time
> steps
> >> in the past because of Gear).
> >> Don't clone the CKT data structure, otherwise you will clone all the
> >> NGSPICE core.
> >>
> >> Regards,
> >> Fra
> >>
> >>
> >> Il giorno 05/nov/2012, alle ore 12:02, Stefano Perticaroli <
> >> spe...@gm...> ha scritto:
> >>
> >>
> >>
> >> 2012/11/5 Yash Dosi <yas...@gm...>
> >>
> >>> Hey Stefano,
> >>>
> >> Hi Yash,
> >>
> >>> Thanks for the reply.
> >>> But after reading your reply I think I started in the wrong direction.
> >>> Let me rephrase my objective. My target is to modify numerical
> integration
> >>> in ngspice using threads, also my primary goal is to just use threads
> in
> >>> the Gear Method's implementation in ngspice.
> >>> I have already explained how I intend to introduce threads in this
> >>> modification in my previous mail. It is something like forward
> pipelining.
> >>>
> >> IMHO for Gear Methods you need at least three accepted time points in
> >> past to compute the next one.
> >>
> >> I mean, every consequent time step depends on the previous ones.  The
> >> more higher order for integration to use, the longer time accuracy in
> the
> >> past you need.
> >>
> >> As I told you before, since the algorithm for time evolution is
> >> implicitly 'serial and heuristic' I think parallelization cannot be
> based
> >> on prediction in the general case.
> >>
> >> The only thing you can imagine is to test in a parallel way the
> >> efficiency of different integration methods.
> >>
> >> Regards.
> >>
> >>> Extending this to trapezoidal Method's implementation is desirable but
> >>> not compulsory.
> >>>
> >>> I started with DCtran because I thought that was one of the places
> where
> >>> Gear Method was used.
> >>> But I think that was not the correct place to start.
> >>>
> >>> Can you please now point me in the correct direction.
> >>> On Nov 5, 2012 3:04 PM, "Stefano Perticaroli" <spe...@gm...>
> >>> wrote:
> >>>
> >>>>
> >>>>
> >>>> 2012/11/5 Yash Dosi <yas...@gm...>
> >>>>
> >>>>> Hello People!
> >>>>>
> >>>>
> >>>> Hi Yash,
> >>>>
> >>>>
> >>>>> As a part of my project I am trying to modify the DCtran Analysis
> >>>>> using threads.
> >>>>> This is my idea so far..
> >>>>>
> >>>>
> >>>> since I'm involved in the modifying of the DCtran for PSS Analysis I
> >>>> try to point out some considerations to your idea.
> >>>>
> >>>>
> >>>>>
> >>>>> 1. Create a duplicate instance of ckt.
> >>>>> 2. Obtain an approximate solution of the current time point.
> >>>>> (terminating the NIiter call early).
> >>>>> 3. Use this approximate solution to calculate a future time point
> >>>>> using the duplicate instance.
> >>>>> 4. Check the convergence conditions and then accept or reject the
> >>>>> computed solutions.
> >>>>>
> >>>>
> >>>> In Transient Analysis there are two convergence conditions checked at
> >>>> any time step: the first one regards the DC solution needed to
> calculate
> >>>> their operating point, the second one regards the truncation error of
> >>>> integrator's time evolution.
> >>>>
> >>>> The NIiter is about the operating point, it is in fact called in
> >>>> CKTop.c (that in turn is called by DCop.c).
> >>>>
> >>>> When you terminate the NIter early, even if one of devices is solved
> >>>> into a different operating mode, the next time step (what you call
> >>>> 'future') is certainly wrong and it could also never converge.
> >>>>
> >>>>
> >>>>
> >>>>> And this is my doubt:
> >>>>> Do I need to create a duplicate of the entire ckt structure. (Because
> >>>>> it will only result in more memory usage and addition of redundant
> code
> >>>>> which will slow the entire process down.)?
> >>>>>
> >>>>
> >>>> The CKT structure contains a lot of things. You would need to consider
> >>>> the CKTmatrix only for solving operating points and integrating time
> >>>> evolution, however the CKTmatrix, as it is actually written in the
> code,
> >>>> requires a quite complete CKT structure.
> >>>>
> >>>> The duplication process of a CKT is not a simple task and Ngspice (and
> >>>> so Spice) was not properly developed for that.
> >>>>
> >>>> If you need some hints about parallelization you could ask to
> Francesco
> >>>> Lannutti, he worked on this subject.
> >>>>
> >>>> Regards.
> >>>>
> >>>>
> >>>>
> >>>>>
> >>>>> Also if I do not need to create a copy the entire ckt instance then
> >>>>> which parts do i need to copy of how do I know which parts are
> required to
> >>>>> be copied?
> >>>>>
> >>>>>
> >>>>>
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