Up: ARPACK subroutines
The subroutine Xgetv0 is responsible for generating starting
vectors. It is called upon to construct the initial Arnoldi/Lanczos vector
when this option is requested. Xgetv0 is also called upon to generate
a new basis vector when the re-orthogonalization scheme of XYaitr
calls for this, i.e. when an invariant subspace is encountered early during
the construction of the Arnoldi factorization. In the latter case,
the vector that is returned by Xgetv0
is already orthogonalized against the existing set of basis vectors. In either
case, if the (shift-invert) computational mode calls for it, the vector
is also forced to be in the range of OP.
The LAPACK subroutine Xlarnv is used to generate the random vectors.
Subroutine Xgetv0 is called by XYaup2 and XYaitr.