[SI-LIST] Re: non-negative off diagonal capacitive matrix elements ??
- From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 4 Sep 2001 13:07:40 -0700
which brings into another question,
ray,
was the tool using FEM (most likely using ICCG) or
BEM (most likely using LU)?
chris
-----Original Message-----
From: Steve Corey [mailto:steve@xxxxxxxxxxxxxx]
Sent: Tuesday, September 04, 2001 12:23 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: non-negative off diagonal capacitive matrix
elements ??
The most common reason for limited precision when inverting a matrix is
that the condition of the matrix to be inverted was poor. This problem
affects both interative methods, such as conjugate gradient, and direct
methods such as LU decomposition. Most coders, if an iterative method
such as ICCG is convergent, will get it to converge as tightly as
possible, and the limit is imposed by the condition of the matrix.
A poorly conditioned matrix is one that is close to singular in the
presence of the computer's roundoff error. Poor conditioning can be a
property of the problem to be solved, and/or a property of the algorithm
used to solve the problem.
Naive as it may sound, I would suspect that in this case that it's due to
the problem being solved. Standard disclaimers apply, however: it's
been quite a few years since I've written any field solver code.
-- 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
-------------------------------------------
Chris Cheng wrote:
> i always wonder if the matrix is inverted through implicit
> method such as ICCG instead of explicit LU deposition, will
> the round off error still produce +ve off diagonal C elements.
> chris
>
> -----Original Message-----
> From: Ray Anderson [mailto:Raymond.Anderson@xxxxxxx]
> Sent: Friday, August 31, 2001 3:43 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: non-negative off diagonal capacitive matrix
> elements ??
>
> Thanks to all who responded on my question of non-negative
> off diagonal elements in a capacitance matrix.
>
> As I thought, the concensus opinion was that the very small
> positive number was down in the numerical noise and is essentially
> a zero entry in the matrix.
>
> Thanks again.
>
> -Ray
>
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