Hi Paul, I don't really like a function that gives different answers for the very same input. That sounds like a bug to me. That being said, from the data you showed, it is not clear that your eigenvector are really different. If what you show is just a difference in the norm of the difference between the eigenvalue at iteration 1 and N, that might be OK. Indeed, if v is an eigenvector, a.v with a non zero-scalar, is also an eigenvector. You should check whether v1 and vN are colinear: if they are, the results are not really different, they just differ by a scaling factor. But I would still call it a bug, as a function should always give the same answer when given the same input parameters.
Cheers, Antoine Le Jeudi 25 Juin 2015 17:17 CEST, "Carrico, Paul" <paul.carr...@esterline.com> a écrit: > 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 > _______________________________________________ > users mailing list > users@lists.scilab.org > http://lists.scilab.org/mailman/listinfo/users > _______________________________________________ users mailing list users@lists.scilab.org http://lists.scilab.org/mailman/listinfo/users
