# bifurcation buckling

## Buckling and Post buckling of Plates

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Hello every one.

I'm doing work on buckling  analysis using abaqus. I want to continue my work on postbuckling of plates also. I'm not getting any tutorials on how to perform Postbuckling analysis of plates using abaqus. When i searched the abaqus help documentation, i got .inp file of a plate, but i didnt get the steps on how to perform the analysis.

I read in some books that after buckling of a plate, it still can take the load. How to do this in abaqus interface ?how to perform the postbuckling analysis in a proper way ?

Plz help

## Bathe's subspace iteration, how to find the largest eigenvalue/mode?

Does anyone know how to modify Bathe's subspace iteration eigensolver to compute the highest eigenvalue instead of the smallest ?

## Subspace Iteration eigenvalues and eigenvectors--efficient implementation?

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Anyone knows an efficient implementation of the subspace iteration method to compute a few lower eigenvalues and eigenvectors of a generalized problem KG*u=lambda*KS*u or any similar method? i.e., to compute the buckling loads and modes.

I'd like to use something optimized to Intel or amd64 processors or similar, like MKL, etc.

This is for bifurcation buckling analysis. KG is the stiffness matrix. KS is the geometric stress matrix. Both constructed from a FEM discretization.

## Math Kernel Library MKL

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I want to use Intel Math Kernel Library (MKL) to calculate the bifurcation loads and modes in my custom FE program. MKL has many algorithms and I want to use the most efficient one.
Basically, I need to find a few eigenvalues lambda_i and eigenvectors u_i for the problem
KG * u = lambda * KS * u
where KG is the stiffness matrix and KS is the geometric stiffness matrix, also called stress-displacement matrix.
Is KG supposed to be positive definite?