.. _IUPD:

``IUPD``
========

````

IUPD is used only in the EF routine. ``IUPD`` should very rarely be
touched. ``IUPD`` controls how the Hessian is updated. Values for
``IUPD`` are 0: skip the update; 1: Use Powell's method; 2: use the BFGS
update. For more information, see `Description of EF and
TS <EigenFollowing.html#t_ef>`__.