I think the first thing is to prove the "accuracy" of the tool. If the simulation tool cannot handle simple geometric shapes with know closed form equation solutions...then the accuracy of ANY solution is in question. If however the tool does just fine then one could determine the lower bound of the tool by simple reducing the same model in size until an error occurs. Chas -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Steve Corey Sent: Monday, September 10, 2001 11:19 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: non-negative off diagonal capacitive matrix elements ?? Charles -- Would scaling actually improve the accuracy of this type of problem? Speaking off the top of my head, scaling should compress the response of the system in frequency, but I wouldn't expect it to improve the conditioning of any matrix which would need inversion to compute L or C. If all geometries are scaled equally, don't you just get scaled matrices to invert? Constant scaling of matrixes generally only improves accuracy if you have to add a bunch of them together, which is usually considered to imply a poorly constructed algorithm anyway. Please let me know if I'm missing something here -- I haven't dealt directly with EM field solver algorithms for quite some time. If the problem is one of numerical noise, it's more a problem of dynamic range in the solution, and the fact that accuracy is apparently being lost for entries somewhere between 3 and 5 orders of magnitude smaller than the main diagonal entries. This is most likely due to the conditioning of intermediate matrices in the solution, which I would expect to be the same for both the scaled and unscaled problems. Scaling might help, however if the algorithm in question ignores matrix entries smaller than a certain cutoff value as being negligible. This is not very likely. -- Steve ------------------------------------------- Steven D. Corey, Ph.D. Time Domain Analysis Systems, Inc. "The Interconnect Modeling Company." http://www.tdasystems.com email: steve@xxxxxxxxxxxxxx phone: (503) 246-2272 fax: (503) 246-2282 ------------------------------------------- Charles Grasso wrote: > Before we all get too hung up on this > the values are verry small - this > could be an issue of numerical noise > in the tool. > > I suggest you rescale the model to say > 10x your existing size and re-run the problem. Just check the tool operation > first.. > > Chas > > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of fname lname > Sent: Saturday, September 08, 2001 2:40 PM > To: si-list@xxxxxxxxxxxxx; Raymond.Anderson@xxxxxxx > Subject: [SI-LIST] non-negative off diagonal capacitive matrix elements > ?? > > Hi Folks, > I have a question. Should the coupling coefficients in the maxwell > capacitence matrix always be in the descending order going down along a > column or can the coupling between the 2nd and 3rd element be greater than > between the 1st and 2nd element. > Any help is greatly appreciated. > > Thanks, > Signal Guy. > -- > >I've just extracted the RLGC matrices for 5 coupled > >striplines using Apsimtech RLGC. > > > >As expected, the diagonal elements of the capacitive matrix are > >positive capacitance values. All the off-diagonal elements are > >negative EXCEPT one. Is this correct. It has been a while since I've > >thought about this, but I was under the impression the capacitive > >off diag element were all negative. Anyone know for sure ?? > > > >The element in column 1 row 5 is the one I question: > > > > > > 3.1600e-15 > > -4.9360e-16 3.2540e-15 > > -2.0080e-17 -4.8990e-16 3.2540e-15 > > -1.3380e-18 -1.9820e-17 -4.8990e-16 3.2540e-15 > > 3.1280e-20 -1.3380e-18 -2.0080e-17 -4.9360e-16 3.1600e-15 > > > > > > > > > >-Ray > > > >------------------------------------------------------------------ > >To unsubscribe from si-list: > >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >For help: > >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > >List archives are viewable at: > > //www.freelists.org/archives/si-list > >or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > >Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > Get 250 color business cards for FREE! > http://businesscards.lycos.com/vp/fastpath/ > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu