[Scilab-users] eigs calculation

[Carrico, Paul]

Dear all

I'm still working on my "eigs" issue topic and I'm still trying to understand what's going wrong;

I run a test case :
- same function is launched 10 times
- each time the input data are recorded (K,M)
- for each loop the eigenvalues u and the eigenvectors v are recorded

Then the values of each loop are compared with the values of the loop 1

If K,M,u remains strictly identical, it is not the case for u (the eigenvectors) ... why ?

I've ever check any initialization issue, but everything seems to be ok

Paul

PS : the results of this case

Max delta v2 - v1 = 453.857
Max delta K2 - K1 = 0
Max delta M2 - M1 = 0

Max delta v3 - v1 = 549.214
Max delta K3 - K1 = 0
Max delta M3 - M1 = 0

Max delta v4 - v1 = 585.95
Max delta K4 - K1 = 0
Max delta M4 - M1 = 0

Max delta v5 - v1 = 379.702
Max delta K5 - K1 = 0
Max delta M5 - M1 = 0

Max delta v6 - v1 = 489.844
Max delta K6 - K1 = 0
Max delta M6 - M1 = 0

Max delta v7 - v1 = 439.221
Max delta K7 - K1 = 0
Max delta M7 - M1 = 0

Max delta v8 - v1 = 432.406
Max delta K8 - K1 = 0
Max delta M8 - M1 = 0

Max delta v9 - v1 = 351.752
Max delta K9 - K1 = 0
Max delta M9 - M1 = 0

Max delta v10 - v1 = 554.515
Max delta K10 - K1 = 0
Max delta M10 - M1 = 0

-----Message d'origine-----
De : Carrico, Paul
Envoyé : mercredi 17 juin 2015 22:18
À : International users mailing list for Scilab.
Objet : RE: [Scilab-users] eigs calculation

Dear All

Thanks for the answers.

To give more information's on what I'm doing (That's quite new I confess), I'm performing  a (basic) finite element calculation with beams using sparse matrix (stiffness matrix K and mass matrix M).
[u,v] = eigs(K((ddl_elem+1):$,(ddl_elem+1):$),M((ddl_elem+1):$,(ddl_elem+1):$),n,"SM");

Nota: ddl means dof

I'm calculated first the natural frequencies using (K - omega^2.M).x=0 ... the pulse (or circular frequencies)  are no more and no less than the eigenvalues of the above system (u = omega^2).

Just a "mechanical" remark: since the beam is clamped in one side (and free on the tip),  it is absolutely normal that you find twice the same natural frequency (1rst mode in one direction, the second one in a new direction at 90°) .... I've been really surprised to find it, but happy at the same time ...

The origin of my question was: since it obvious that the results are strongly sensitive to the "units" (i.e. the numbers), I'm wondering if there is a way to control the accuracy of the eigenvalues calculation using eigs keywords ... 

In any way, thanks for the debate

Paul

EXPORT CONTROL : 
Cet email ne contient pas de données techniques
This email does not contain technical data