On 05/03/2012 07:55 PM, Russ P. wrote:
On May 3, 10:30 am, someone<newsbo...@gmail.com> wrote:
On 05/02/2012 11:45 PM, Russ P. wrote:
For any practical engineering or scientific work, I'd say that a
condition number of 1e6 is very likely to be completely unacceptable.
So how do you explain that the natural frequencies from FEM (with
condition number ~1e6) generally correlates really good with real
measurements (within approx. 5%), at least for the first 3-4 natural
frequencies?
I would say that the problem lies with the highest natural frequencies,
they for sure cannot be verified - there's too little energy in them.
But the lowest frequencies (the most important ones) are good, I think -
even for high cond number.
Did you mention earlier what "FEM" stands for? If so, I missed it. Is
it finite-element modeling? Whatever the case, note that I said, "If
Sorry, yes: Finite Element Model.
you are just doing pure mathematical or numerical work with no real-
world measurement error, then a condition number of
1e6 may be fine." I forgot much more than I know about finite-element
modeling, but isn't it a purely numerical method of analysis? If that
I'm not sure exactly, what is the definition of a purely numerical
method of analysis? I would guess that the answer is yes, it's a purely
numerical method? But I also thing it's a practical engineering or
scientific work...
is the case, then my comment above is relevant.
Uh, I just don't understand the difference:
1) "For any practical engineering or scientific work, I'd say that a
condition number of 1e6 is very likely to be completely unacceptable."
vs.
2) "If you are just doing pure mathematical or numerical work with no
real-world measurement error, then a condition number of, 1e6 may be fine."
I would think that FEM is a practical engineering work and also pure
numerical work... Or something...
By the way, I didn't mean to patronize you with my earlier explanation
of orthogonal transformations. They are fundamental to understanding
the SVD, and I thought it might be interesting to anyone who is not
familiar with the concept.
Don't worry, I think it was really good and I don't think anyone
patronized me, on the contrary, people was/is very helpful. SVD isn't my
strongest side and maybe I should've thought a bit more about this
singular matrix and perhaps realized what some people here already
explained, a bit earlier (maybe before I asked). Anyway, it's been good
to hear/read what you've (and others) have written.
Yesterday and earlier today I was at work during the day so
answering/replying took a bit longer than I like, considering the huge
flow of posts in the matlab group. But now I'm home most of the time,
for the next 3 days and will check for followup posts quite frequent, I
think...
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