[SI-LIST] Re: non-negative off diagonal capacitive matrix elements ??
- From: Steve Corey <steve@xxxxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 10 Sep 2001 10:19:17 -0700
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
> >
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