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From: Stefan Jahn <stefan@gr...>  20071229 12:59:52

Am Sa, 29.12.2007, 13:27, schrieb Bastien ROUCARIES: Hello! > In fact I know a world class specialist of precondionning and inversion > problem. He is sitting in the building near me at uni. I will try to talk > to > him about the problem. > > Could you give me some pointer to documentation? He is a pure math guy, so > in > order to have a quick and efficient tip, we need to ask him a mathematical > question. THerefore could you explain fully the problem? It is something like this: * equation systems can be solved with different solvers (e.g. LU, QR, SVD, inversion, etc.) * the given matrix and right hand side can be modified (exchanging columns or rows) without chaning the euqation system * during some of the solution algorithms pivoting is used; this leaves also a degree of freedom (pivot element can be choosen) * the method, matrix order as well as the pivotstrategy give slightly different results due to numerical errors Thus the question is: Is there a preconditionmethod which allows a solver to solve the equation system more accurate (even for almost singular matrices). I think a precondition always must consider which solver/decomposer is used and also which pivotstrategy is used. Hope this is a question in fact, Stefan. 
From: Stefan Jahn <stefan@gr...>  20071229 12:31:37

Am Mo, 8.10.2007, 18:31, schrieb Markus Mettenleiter: > Dear QUCS team, Hi! And sorry for the very looooong delay. > Since I'm currently dealing with BJT noise (in a very low noise TIA > application), I had a closer look at the BJT noise model (fig. 10.15) > and related equations. The noise sources ib^2 and ic^2 from equations > 10.145 and 10.146 are very clear to me, but how do the contributions of > the ohmic resistances Rbb, Rc, Re (equ. 10.144) fit into the figure > 10.15 noise model ? None of the terms shows up there, but at least Rbb > can not be neglected for a decent noise calculation. > > To my knowledge the noise contribution of Rbb can be regarded as voltage > source with ubb^2 = 4KTRbb and placed in series with Rbb of figure > 10.10. But what about the noise contributions of Rc and Re  convert > them into voltage sources and place them in series with Rc and Re of the > figure 10.10 model as well ? However, it's not quite clear from this > document, what the simulator actually calculates.... The noise current in parallel to the resistances Rbb, Re and Rc are computed as 10.144 states. The figure 10.15 leaves them, because it only shows the "intrinsic BJT". > So could you please enhance the fig. 10.15 noise model with the Rbb, Rc, > Re noise sources  or let me know what I overlooked ! Well, I think it's so very easy, that we decided to leave that. I am not yet unsure if I should really add these... Cheers, Stefan. 
From: Stefan Jahn <stefan@gr...>  20071229 12:24:35

Am Sa, 29.12.2007, 13:20, schrieb Bastien ROUCARIES: Hello! >> > I'm still playing around with multivibrators in transient simulation. >> > This one is nice: attached you will find two identical schematics >> which >> > produce almost the same netlist. The only difference between the >> netlists >> > is the order of the statements. But the results of the transient >> > simulation are very different. (the first one fails after producing >> > moreorless accurate results and the other one runs thru but nothing >> > vibrates..) >> > >> > I think the problem is that in the 2nd case the evaluation order of >> the >> > nodes is different so the transistor is evaluated after the value of >> its >> > base contact has been calculated, overwriting the initial DC value I >> have >> > set using the label. Which is quite strange because I thought that my >> > label >> > would cause the initial dc analyses to charge the capacitor on this >> wire >> > so >> > the wire should stay longer on a high voltage that just for step 0. >> > >> > Whats the error in my understanding of what's going on when doing a >> > transient simulation of this circuit? >> >> This one is also known... And an ugly one, I know. >> >> Right now the position in the netlist in fact determines somehow, how >> nodes are put into the circuit matrix to be solved which in turn may >> affect the result due to numerical issues. >> >> One of the solution of this problem may be to find a way to reorder >> the matrix to be solved in a way to >> >> 1) get a deterministic ordering >> 2) and find an order which makes the matrix "easier" to solve >> >> If someone on the list has a better clue than me right now how to >> achieve (2) then please tell me. In the qucsator core there is >> already an sorting algorithm, but this just cares about pairs of >> +1 and 1 (e.g. voltage sources) and not about the actual node >> order... > > Could you please give me the equation to solve? > I suppose it is an inversion. Some of the implemented equation system solvers (e.g. LU, QR, SVD) decompose the matrix, then solve the system using additionally the righthand side... > IF so the magic key is preconditionning. I know :))) > I can try to help when I will come back form vaccation (ie 2008/01/08). If you have some preconditionknowledge I would be glad if you can share it... Cheers, Stefan. 
From: Bastien ROUCARIES <roucaries.bastien@gm...>  20071229 12:19:01

Le samedi 29 d=E9cembre 2007, Stefan Jahn a =E9crit=A0: > Am Mi, 26.12.2007, 09:15, schrieb Clifford Wolf: > > Hi, > > Hello! > > > I'm still playing around with multivibrators in transient simulation. > > This one is nice: attached you will find two identical schematics which > > produce almost the same netlist. The only difference between the netlis= ts > > is the order of the statements. But the results of the transient > > simulation are very different. (the first one fails after producing > > moreorless accurate results and the other one runs thru but nothing > > vibrates..) > > > > I think the problem is that in the 2nd case the evaluation order of the > > nodes is different so the transistor is evaluated after the value of its > > base contact has been calculated, overwriting the initial DC value I ha= ve > > set using the label. Which is quite strange because I thought that my > > label > > would cause the initial dc analyses to charge the capacitor on this wire > > so > > the wire should stay longer on a high voltage that just for step 0. > > > > Whats the error in my understanding of what's going on when doing a > > transient simulation of this circuit? > > This one is also known... And an ugly one, I know. > > Right now the position in the netlist in fact determines somehow, how > nodes are put into the circuit matrix to be solved which in turn may > affect the result due to numerical issues. > > One of the solution of this problem may be to find a way to reorder > the matrix to be solved in a way to > > 1) get a deterministic ordering > 2) and find an order which makes the matrix "easier" to solve > > If someone on the list has a better clue than me right now how to > achieve (2) then please tell me. In the qucsator core there is > already an sorting algorithm, but this just cares about pairs of > +1 and 1 (e.g. voltage sources) and not about the actual node > order... Could you please give me the equation to solve? I suppose it is an inversion. IF so the magic key is preconditionning. I can try to help when I will come back form vaccation (ie 2008/01/08). Regards=20 Bastien > Cheers, Stefan. > > >  > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2005. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Qucshelp mailing list > Qucshelp@... > https://lists.sourceforge.net/lists/listinfo/qucshelp =2D=20 "ROUCARIES Bastien" roucaries.bastien@...= com =2D= =2D DO NOT WRITE TO roucaries.bastien+blackhole@... OR BE BLACKLISTED 
From: Stefan Jahn <stefan@gr...>  20071229 12:13:59

Am Fr, 14.12.2007, 12:22, schrieb Doom3d: > Hi, Hello Szalai, > I wanted to use an IRFZ34N enhancement nchannel power MOSFET from the > Mosfet component library. As a first step, I tried to get Id vs Ugs > characteristics. I got immediately some warning messages, telling that > D1,D3,D4 diodes in subcircuitry have unphysical N<1 parameters. > > After modifying N values to 1.04, it works w/o errors, but I am not > sure, that the characteristic curves are still valid. The warnings are ok. Don't care. Changing the values will give you different characteristics in fact. > Actually I wanted to create a Luxeon Rebel LED+ dynamo based bycycle > lighting circuitry, including a hybrid rectifier bridge (mosfets on low > side, schottky's on high side) using BUK923755A. I wanted to base my > BUK9237 def file on IRFZ34N.. :))) > BTW, I created a Luxeon Rebel white LED 1.5A def by curve fitting, but > am not sure, that my parameters are physically correct, and also don't > know real Id values for Uf<3V. It is based on the 20mA red LED def. > Please, could You have a look on it? I'll give a look later... Cheers, Stefan. PS: Sorry for the looooooooooooong delay... 
From: Stefan Jahn <stefan@gr...>  20071229 12:07:58

Am Mi, 26.12.2007, 09:15, schrieb Clifford Wolf: > Hi, Hello! > I'm still playing around with multivibrators in transient simulation. This > one is nice: attached you will find two identical schematics which produce > almost the same netlist. The only difference between the netlists is the > order of the statements. But the results of the transient simulation are > very different. (the first one fails after producing moreorless accurate > results and the other one runs thru but nothing vibrates..) > > I think the problem is that in the 2nd case the evaluation order of the > nodes is different so the transistor is evaluated after the value of its > base contact has been calculated, overwriting the initial DC value I have > set using the label. Which is quite strange because I thought that my > label > would cause the initial dc analyses to charge the capacitor on this wire > so > the wire should stay longer on a high voltage that just for step 0. > > Whats the error in my understanding of what's going on when doing a > transient simulation of this circuit? This one is also known... And an ugly one, I know. Right now the position in the netlist in fact determines somehow, how nodes are put into the circuit matrix to be solved which in turn may affect the result due to numerical issues. One of the solution of this problem may be to find a way to reorder the matrix to be solved in a way to 1) get a deterministic ordering 2) and find an order which makes the matrix "easier" to solve If someone on the list has a better clue than me right now how to achieve (2) then please tell me. In the qucsator core there is already an sorting algorithm, but this just cares about pairs of +1 and 1 (e.g. voltage sources) and not about the actual node order... Cheers, Stefan. 
From: Stefan Jahn <stefan@gr...>  20071229 12:00:24

Am Mi, 26.12.2007, 11:39, schrieb Clifford Wolf: > Hi, Hello! > when I create a subcircuit in which I simply connect ports without any > devices in between, the simulation gives me bogus results. It works fine > with zeroresistance resistors thought. > > So the following netlist does not work: > > snip > .Def:xwire _net0 _net0 _net1 _net1 > .Def:End > snap > > While this one is working fine: > > snip > .Def:xwire _net0 _net1 _net2 _net3 > R:R1.0 _net1 _net0 R="0" > R:R2.0 _net3 _net2 R="0" > .Def:End > snap > > Here is the full working netlist: > > snip > # Qucs 0.0.12 /home/clifford/.qucs/DEMO_prj/xwire_test.sch > > .Def:xwire _net0 _net1 _net2 _net3 > R:R1.0 _net1 _net0 R="0" > R:R2.0 _net3 _net2 R="0" > .Def:End > > Vdc:V1 _net0 _net1 U="1 V" > .TR:TR1 Type="lin" Start="0" Stop="1 ms" Points="11" > IntegrationMethod="Trapezoidal" Order="2" InitialStep="1 ns" > MinStep="1e16" MaxIter="150" reltol="0.001" abstol="1 pA" vntol="1 uV" > Temp="26.85" LTEreltol="1e3" LTEabstol="1e6" LTEfactor="1" > Solver="CroutLU" relaxTSR="no" initialDC="yes" MaxStep="0" > VProbe:Pr2 _net2 _net3 > R:R1 _net3 _net2 R="4 Ohm" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85" > IProbe:Pr1 _net7 _net2 > R:R2 _net6 _net7 R="1 Ohm" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85" > Sub:XWire1 _net0 _net4 _net1 _net5 Type="xwire" > Sub:XWire2 _net5 _net3 _net4 _net6 Type="xwire" > snap This one, about the "two or more subcircuit ports, but same node", is known already. I've not yet come to an implemented solution, but it is on my todo list. Thanks for reporting, Stefan. 
From: Stefan Jahn <stefan@gr...>  20071229 11:49:48

Am Do, 27.12.2007, 01:40, schrieb Clifford Wolf: > Hi again, Hello Clifford! >> > Are there any plans to add noise sources to transient simulation? With >> > a random seed as optional parameter so there is 'reproduceable >> > randomness' to would be nice.. ;) >> >> Not yet. Let me think about this... > > I've just seen on the webpage that there is a random() function in CVS. Do > I guess right that this could be used in an eq defined device to create a > noice current source  and thus create a noice voltage source by adding > a current controlled voltage source, or by adding a parallel resistor if > the voltage source doesn't need to be an ideal voltage source (Norton's > theorem)? Hm. You may give it try in fact... Cheers, Stefan. 