The parameter `info` should be set to `0` on the initial call to
`dsaupd` unless the user wants to supply the starting vector that
initializes the IRLM. Normally, this default is a reasonable
choice. However, if this eigenvalue calculation is one of a sequence
of closely related problems then convergence may be accelerated
if a suitable starting vector is specified. Typical choices in this situation
might be to use the final value of the starting vector from the
previous eigenvalue calculation (that vector will already
be in the first column of `V`) or to construct a starting vector
by taking a linear combination of the computed eigenvectors
from the previously converged eigenvalue calculation. If the starting
vector is to be supplied, then it should be placed in the array
`resid` and `info` should be set to `1` on entry
to `dsaupd`. On completion, the parameter `info` may contain the
value `0` indicating the iteration was successful or it may contain a
nonzero value indicating an error or a warning condition. The meaning of a
nonzero value returned in `info` may be found in the header comments of
the subroutine `dsaupd`.