Solving ARPACK with INFO = 3: Seek Help Here!

[NeoDevin]

I'm using ARPACK to find the eigenvalues of a matrix, it works for some of the problems I need it for, but for others, it returns INFO = 3, which means:

No shifts could be applied during a cycle of the implicitly restarted Arnoldi iteration. One possibility is to increase the size of NCV relative to NEV. See remark 4 below.

Remark 4 says:

At present there is no a-priori analysis to guide the selection of NCV relative to NEV. The only formal requrement is that NCV > NEV. However, it is recommended that NCV .ge. 2*NEV. If many problems of the same type are to be solved, one should experiment with increasing NCV while keeping NEV fixed for a given test problem. This will usually decrease the required number of OP*x operations but it also increases the work and storage required to maintain the orthogonal basis vectors. The optimal "cross-over" with respect to CPU time is problem dependent and must be determined empirically.

I have tried increasing NCV, and playing with the values of both NEV and NCV, but no luck.

Anyone who has worked with ARPACK, and knows how to solve this problem, your help would be greatly appreciated.

 

[NeoDevin]

Anyone? I'm kinda stuck here, I can't move on until I get this working, and no one around here seems to know why it's doing it, or how to fix it.

 

[ravenprp]

Thank you for reaching out for help with your issue in using ARPACK to find eigenvalues. It seems that you have already taken the necessary steps by increasing NCV and experimenting with the values of NEV and NCV. However, as stated in Remark 4, the optimal values for these parameters may vary depending on the specific problem you are trying to solve. It is recommended to continue experimenting with different combinations of NCV and NEV until you find a suitable solution.

Additionally, you may want to consider seeking help from others who have experience using ARPACK. You can reach out to online forums or communities dedicated to numerical computing and seek advice from experts in this field. They may be able to provide insights or suggestions on how to approach and solve your problem.

In conclusion, don't hesitate to seek help when facing difficulties in using ARPACK. With the help of others, you may be able to find a solution and successfully solve your problem. Good luck!