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.