Linear buckling mode order

[dozer]

I'm curious how other FEA programs report linear (eigenvalue) buckling modes. I've used COSMOS/M for several years and it reports the eigenvalues in numerical order. In other words, if you asked for six modes you might get something like:

Mode Value
1 -5.1
2 -3.2
3 2.6
4 3.0
5 4.5
6 7.8

SAP2000 reports them in absolute order. So with the same problem you would get:

Mode Value
1 2.6
2 3.0
3 -3.2
4 4.5
5 -5.1
6 7.8

Now before some of you say "If you would have only asked for two modes in COSMOS/M you would have missed a critical mode!" Don't worry, they aren't that dumb. ;-) It "centers" the results around zero. You would have got 1=2.6 and 2=3.0. You can actually use what they call a "shift" to change this but I digress.

So, my question is how do other programs report eigenvalues?

In case you're wondering why I'm asking, it seems like this is something that should be consistent. I almost missed an important positive eigenvalue in SAP buried among a bunch of negatives because I was used to the COSMOS way. Yes, I know that SAP allows you to sort them. Yes, now that I realize how it does it, it's no big deal. I'm just curious.

 

[johnhors]

Dozer

SAP2000 appears to be the odd one out as I've used about all of the major systems at one time or another and they all by default report eigenvalues in numerically ascending order.

 

[dozer]

We also have Robot Millenium. Guess what, it reports it like SAP does, in ascending order of absolute values.

Keep those cards and letters coming.

 

[jhardy1]

For what it's worth, I use Strand7. It lists buckling modes in ascending order of absolute values, like SAP and Robot. To me, this is the most "useful" way to present the Eigenvalues, because I am more likely to be interested in values close to zero (small load magnitude) than I am in very large negative load multipliers.

THE FIRST 10 EIGENVALUES HAVE CONVERGED

FINAL BUCKLING RESULTS
CALCULATED BUCKLING LOAD FACTORS
1 -1.13813971E+00
2 1.50137570E+00
3 6.37902274E+00
4 -8.85538958E+00
5 1.01248056E+01
6 1.58579853E+01
7 -1.82721600E+01
8 1.95350509E+01
9 2.37272283E+01
10 -2.55458952E+01