Hi,
I am new to MAGMA. I want to find the top K(K is a very small number) eigen vectors of a sparse symmetric matrix whose dimension is more than 30000. In addition, the matrix in consideration is positive semi definite. However, I am not able to understand the arguments that needs to be passed to the magma_slobpcg function for the magma_s_solver_par and the magma_s_preconditioner structures. I wanted to know the parameters that I have to set as a minimum requirement. Also, what parameters that i could enable to perform the calculations faster?
Thanks in advance,
Nithish
LOBPCG method for Eigen Value Computation.

 Posts: 90
 Joined: Tue Sep 02, 2014 5:44 pm
Re: LOBPCG method for Eigen Value Computation.
Dear Nithish,
for a plain LOBPCG, use ./testing_dsolver solver 8 ev k /path/to/the/matrix
If you want to use a preconditioner (faster solver convergence in many cases) type
./testing_dsolver solver 8 ev k precond x /path/to/the/matrix
where x = 1 is Jacobi, x = 2 is ILU.
Let me know whether this helps!
Thanks, Hartwig
for a plain LOBPCG, use ./testing_dsolver solver 8 ev k /path/to/the/matrix
If you want to use a preconditioner (faster solver convergence in many cases) type
./testing_dsolver solver 8 ev k precond x /path/to/the/matrix
where x = 1 is Jacobi, x = 2 is ILU.
Let me know whether this helps!
Thanks, Hartwig

 Posts: 6
 Joined: Sun Oct 12, 2014 6:01 am
Re: LOBPCG method for Eigen Value Computation.
Hi Hartwig,
Thanks for the reply. I tried the use the solver using the method suggested by you and it helped me to find the eigenvalues correctly. However instead of providing the klargest eigen values, it provides me with Ksmallest ones. Is there a setting for the algorithm which calculates the largest eigen values?
With regards,
Nithish
Thanks for the reply. I tried the use the solver using the method suggested by you and it helped me to find the eigenvalues correctly. However instead of providing the klargest eigen values, it provides me with Ksmallest ones. Is there a setting for the algorithm which calculates the largest eigen values?
With regards,
Nithish

 Posts: 281
 Joined: Fri Aug 21, 2009 10:39 pm
Re: LOBPCG method for Eigen Value Computation.
Nithish,
We haven't provided explicitly an option for that but if you compute the eigenvalues for A, and multiply the result by 1 at the end, you will get the set of the largest eigenvalues for A.
Best regards,
Stan
We haven't provided explicitly an option for that but if you compute the eigenvalues for A, and multiply the result by 1 at the end, you will get the set of the largest eigenvalues for A.
Best regards,
Stan

 Posts: 6
 Joined: Sun Oct 12, 2014 6:01 am
Re: LOBPCG method for Eigen Value Computation.
Thanks for the info, Stan