Driver zndrv1 solves the standard eigenvalue problem
This mode only requires matrix vector products with This driver will compute the eigenvalues of largest or smallest magnitude, largest or smallest real part, largest or smallest imaginary part depending on the setting of which. It is most appropriate for computing extremal, non-clustered eigenvalues (here extremal means extreme points of the convex hull of the spectrum). In particular, if the operation can be easily formed, then using the shift-invert driver zndrv2 with zero shift is certainly a far more effective way to compute eigenvalues of the smallest magnitude.