We have some sims that run absurdly slow. What are your favorite speedups? In LT spice, I have arbitrarily done .opt reltol=.002 .opt abstol=5n .opt trtol=5 but that's just guessing. It may work with my parts but mess up an encrypted model that I have no visibility into. Sometimes one solver is unaccountably better than another.
favorite Spice speedups
Started by ●October 24, 2022
Reply by ●October 25, 20222022-10-25
On Mon, 24 Oct 2022 13:16:20 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:>We have some sims that run absurdly slow. What are your favorite >speedups? > >In LT spice, I have arbitrarily done > >.opt reltol=.002 > >.opt abstol=5n > >.opt trtol=5 > >but that's just guessing. It may work with my parts but mess up an >encrypted model that I have no visibility into. > >Sometimes one solver is unaccountably better than another.Straight from LTwiki ... Was probably from my friend, David Edwards, AKA Analog Spiceman... https://ltwiki.org/index.php?title=Main_Page .options gmin=1e-10 .options abstol=1e-10 .options reltol=0.003 .options cshunt=1e-15 boB
Reply by ●October 25, 20222022-10-25
On Mon, 24 Oct 2022 21:31:23 -0700, boB <boB@K7IQ.com> wrote:>On Mon, 24 Oct 2022 13:16:20 -0700, John Larkin ><jlarkin@highland_atwork_technology.com> wrote: > >>We have some sims that run absurdly slow. What are your favorite >>speedups? >> >>In LT spice, I have arbitrarily done >> >>.opt reltol=.002 >> >>.opt abstol=5n >> >>.opt trtol=5 >> >>but that's just guessing. It may work with my parts but mess up an >>encrypted model that I have no visibility into. >> >>Sometimes one solver is unaccountably better than another. > > >Straight from LTwiki ... Was probably from my friend, David Edwards, >AKA Analog Spiceman... > >https://ltwiki.org/index.php?title=Main_Page > > >.options gmin=1e-10 >.options abstol=1e-10 >.options reltol=0.003 >.options cshunt=1e-15 > > >boBThanks, we'll try them. We can run a slow sim, add the hacks, and re-run and see if anything changes much. If not, we can then run the sims that matter. It's taking basically all day to run 50 ms of our power supply sim, and we can't iterate very well at that rate.
Reply by ●October 25, 20222022-10-25
On 10/24/2022 4:16 PM, John Larkin wrote:> We have some sims that run absurdly slow. What are your favorite > speedups? > > In LT spice, I have arbitrarily done > > .opt reltol=.002 > > .opt abstol=5n > > .opt trtol=5 > > but that's just guessing. It may work with my parts but mess up an > encrypted model that I have no visibility into. > > Sometimes one solver is unaccountably better than another. >Using a RAM drive for waveform storage is one, but I guess I don't regularly run sims complex enough that it causes a Ryzen 5600 to chug badly enough to make me frustrated. Have you upgraded your CPU lately?
Reply by ●October 25, 20222022-10-25
On Tue, 25 Oct 2022 10:43:18 -0400, bitrex <user@example.net> wrote:>On 10/24/2022 4:16 PM, John Larkin wrote: >> We have some sims that run absurdly slow. What are your favorite >> speedups? >> >> In LT spice, I have arbitrarily done >> >> .opt reltol=.002 >> >> .opt abstol=5n >> >> .opt trtol=5 >> >> but that's just guessing. It may work with my parts but mess up an >> encrypted model that I have no visibility into. >> >> Sometimes one solver is unaccountably better than another. >> > >Using a RAM drive for waveform storage is one, but I guess I don't >regularly run sims complex enough that it causes a Ryzen 5600 to chug >badly enough to make me frustrated. Have you upgraded your CPU lately?The guy running this for me has a pretty good, fairly new PC. But the sim takes hours to simulate 10s of milliseconds, so we don't want a modest speedup. TI software, TI models, runs for hours. That's silly.
Reply by ●October 25, 20222022-10-25
On Tue, 25 Oct 2022 07:56:38 -0700, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:>On Tue, 25 Oct 2022 10:43:18 -0400, bitrex <user@example.net> wrote: > >>On 10/24/2022 4:16 PM, John Larkin wrote: >>> We have some sims that run absurdly slow. What are your favorite >>> speedups? >>> >>> In LT spice, I have arbitrarily done >>> >>> .opt reltol=.002 >>> >>> .opt abstol=5n >>> >>> .opt trtol=5 >>> >>> but that's just guessing. It may work with my parts but mess up an >>> encrypted model that I have no visibility into. >>> >>> Sometimes one solver is unaccountably better than another. >>> >> >>Using a RAM drive for waveform storage is one, but I guess I don't >>regularly run sims complex enough that it causes a Ryzen 5600 to chug >>badly enough to make me frustrated. Have you upgraded your CPU lately? > >The guy running this for me has a pretty good, fairly new PC. But the >sim takes hours to simulate 10s of milliseconds, so we don't want a >modest speedup. > >TI software, TI models, runs for hours. That's silly.I have had LTspice circuits that would not converge or took enormous amounts of time that were fixed by simple adding high value resistance between isolated nodes or to grounded nodes. Several MegOhms. Those 4 lines I posted seem to help a lot though. Not 100% though. I had one circuit that did not converge until I hung just ONE end of a resistor to a node. The next version of LTspice fixed that issue though. Or, one of the models of one of the parts are the problem. The matrix becomes ill conditioned I guess. It's all dependant on how well the models are created it seems. boB
Reply by ●October 25, 20222022-10-25
On 2022-10-25 19:37, boB wrote:> On Tue, 25 Oct 2022 07:56:38 -0700, John Larkin > <jlarkin@highlandSNIPMEtechnology.com> wrote: > >> On Tue, 25 Oct 2022 10:43:18 -0400, bitrex <user@example.net> wrote: >> >>> On 10/24/2022 4:16 PM, John Larkin wrote: >>>> We have some sims that run absurdly slow. What are your favorite >>>> speedups? >>>> >>>> In LT spice, I have arbitrarily done >>>> >>>> .opt reltol=.002 >>>> >>>> .opt abstol=5n >>>> >>>> .opt trtol=5 >>>> >>>> but that's just guessing. It may work with my parts but mess up an >>>> encrypted model that I have no visibility into. >>>> >>>> Sometimes one solver is unaccountably better than another. >>>> >>> >>> Using a RAM drive for waveform storage is one, but I guess I don't >>> regularly run sims complex enough that it causes a Ryzen 5600 to chug >>> badly enough to make me frustrated. Have you upgraded your CPU lately? >> >> The guy running this for me has a pretty good, fairly new PC. But the >> sim takes hours to simulate 10s of milliseconds, so we don't want a >> modest speedup. >> >> TI software, TI models, runs for hours. That's silly. > > > I have had LTspice circuits that would not converge or took enormous > amounts of time that were fixed by simple adding high value resistance > between isolated nodes or to grounded nodes. Several MegOhms.[...]> > boBThe circuits Spice has trouble with are usually unrealistic, idealized circuits. You can't have ideal floating nodes. There is always a bit of leakage, so insert that resistor. You can't have perfectly conducting loops either. Again, insert some resistance. Also, read the manual (scad3.pdf). Some elements have some parasitics added by default, which may or may not be appropriate in your circuit. You can force them to whatever you deem right, but it takes a bit of experience to be able to judge what *is* right. Jeroen Belleman
Reply by ●October 25, 20222022-10-25
On Tue, 25 Oct 2022 07:56:38 -0700, John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:>On Tue, 25 Oct 2022 10:43:18 -0400, bitrex <user@example.net> wrote: > >>On 10/24/2022 4:16 PM, John Larkin wrote: >>> We have some sims that run absurdly slow. What are your favorite >>> speedups? >>> >>> In LT spice, I have arbitrarily done >>> >>> .opt reltol=.002 >>> >>> .opt abstol=5n >>> >>> .opt trtol=5 >>> >>> but that's just guessing. It may work with my parts but mess up an >>> encrypted model that I have no visibility into. >>> >>> Sometimes one solver is unaccountably better than another. >>> >> >>Using a RAM drive for waveform storage is one, but I guess I don't >>regularly run sims complex enough that it causes a Ryzen 5600 to chug >>badly enough to make me frustrated. Have you upgraded your CPU lately? > >The guy running this for me has a pretty good, fairly new PC. But the >sim takes hours to simulate 10s of milliseconds, so we don't want a >modest speedup. > >TI software, TI models, runs for hours. That's silly.My recollection from my power-system colleagues is that this can be caused by often parasitic sub circuits with very short time constants (compared to the core circuit), so the approach was to model only the core circuit at first, then start to decorate it. Joe Gwinn
Reply by ●October 25, 20222022-10-25
http://www.kevinaylward.co.uk/ee/index.html "John Larkin" wrote in message news:r2uflh18gf75sp7v3m8476u7b79uqql1li@4ax.com... On Tue, 25 Oct 2022 10:43:18 -0400, bitrex <user@example.net> wrote:>On 10/24/2022 4:16 PM, John Larkin wrote: >> We have some sims that run absurdly slow. What are your favorite >> speedups? >> >> In LT spice, I have arbitrarily done >> >> .opt reltol=.002 >> >> .opt abstol=5n >> >> .opt trtol=5 >> >>> but that's just guessing. It may work with my parts but mess up an >>> encrypted model that I have no visibility into. >> >> Sometimes one solver is unaccountably better than another. >> > >>Using a RAM drive for waveform storage is one, but I guess I don't >>regularly run sims complex enough that it causes a Ryzen 5600 to chug >>badly enough to make me frustrated. Have you upgraded your CPU lately?>The guy running this for me has a pretty good, fairly new PC. But the >sim takes hours to simulate 10s of milliseconds, so we don't want a >modest speedup.>TI software, TI models, runs for hours. That's silly.I would have to have a look at it to see about pointing the way to contracting decent behavioural models for the relevant bits I have a current mode SMPS in my SS examples taking 5 secs to do a 200us sim I don't have much confidence in mainstream companies making usable models. It probably needs a rewrite from scratch. You just cant get the staff..... I should get TI to subcontract their models to me :-) Kevin Aylward http://www.anasoft.co.uk/ SuperSpice
Reply by ●October 25, 20222022-10-25
On 25/10/2022 15:42, John Larkin wrote:> On Mon, 24 Oct 2022 21:31:23 -0700, boB <boB@K7IQ.com> wrote: > >> On Mon, 24 Oct 2022 13:16:20 -0700, John Larkin >> <jlarkin@highland_atwork_technology.com> wrote: >> >>> We have some sims that run absurdly slow. What are your favorite >>> speedups? >>> >>> In LT spice, I have arbitrarily done >>> >>> .opt reltol=.002 >>> >>> .opt abstol=5n >>> >>> .opt trtol=5 >>> >>> but that's just guessing. It may work with my parts but mess up an >>> encrypted model that I have no visibility into. >>> >>> Sometimes one solver is unaccountably better than another. >> >> >> Straight from LTwiki ... Was probably from my friend, David Edwards, >> AKA Analog Spiceman... >> >> https://ltwiki.org/index.php?title=Main_Page >> >> >> .options gmin=1e-10 >> .options abstol=1e-10 >> .options reltol=0.003 >> .options cshunt=1e-15 >> >> >> boB > > Thanks, we'll try them. > > We can run a slow sim, add the hacks, and re-run and see if anything > changes much. If not, we can then run the sims that matter.You could try running sims at 4x, 2x and 1x delta_t and use Richardson extrapolation to try and guess at the true solution.> > It's taking basically all day to run 50 ms of our power supply sim, > and we can't iterate very well at that rate.You need to figure out where it is spending all its time. Adding ram might help speed it up as might looking to see which resources are gridlocked. Paradoxically limiting the maximum number of cores it can use might also speed it up or at the very least get the same answer in the same time with less power used. My PC is 4 physical 8 virtual core and is optimal for chess puzzles or spice with 6 cores running. Beyond that it saturates memory bandwidth and all 8 cores is slower than 6! Chances are one or more of the equations is stiff and the time step is becoming infinitessimal on one of the rapid transitions. Adding a bit of spurious dissipation 1M to ground here and there might take the edge off whatever is making it so stiff. We once did some awkward PDE's in a computer solution and on a Tektronix vector display monitor they looked fine so sent them off to the plotter. The job came back part done with an apologetic note from the sysop "your job was cancelled because the red pen began to work loose". Careful examination of the plot file showed some of the vector steps were just Angstroms long! -- Regards, Martin Brown
