If eigenvalues near a point are sought, then one of the shift-invert drivers dndrv4, dndrv5 or dndrv6 should be used. Driver dndrv4 can be used when the shift has a zero imaginary part. Otherwise, either dndrv5 or dndrv6 should be used. To use these drivers, one is required to supply the action ofWhen has a nonzero imaginary part, a complex factorization routine or a complex iterative solver will be required. In that case, the vector will in general be a complex vector. However, only the real or imaginary part will be passed into dnaupd and all arithmetic and data types within the ARPACK routines will be real. In any case, the IRAM will find selected eigenvalues of depending on the setting of which. The recommended setting for computing eigenvalues of the pair () nearest to is which = 'LM'. However, other settings are not precluded.