[SI-LIST] Re: non-negative off diagonal capacitive matrix elements ??
- From: "Charles Grasso" <cgrassosprint1@xxxxxxxxxxxxx>
- To: <steve@xxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 10 Sep 2001 11:41:34 -0600
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
> >
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