Dear all,

I am puzzling with a problem on the setting of input parameters to

LAPACKE_dggevx

namely, ldvr, the size of the leading dimension of the right eigenvectors. It is mentioned in the manual

If jobvr='V', ldvr >= max(1,n)

On a 4 by 4 test problem, if I set ldvr to n it finds the eigenvectors correctly, whereas setting ldvr to 'n+1' does not give me the right eigenvectors. Is not ldvr for allocation purposes only? So why does setting ldvr to 'n+1' brings numerical problems?

More importantly, if I use this function in my code for a large system where an enlarging evp is solved in each iteration(A Lanczos solver btw), it sometimes converges but sometimes not, I am suspecting that this is related to the above mentioned problem.

I could not understand the reason of this strange problem. Will that make a difference if I use FORTRAN 77 interface?

Best,

Umut