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`IPOL`,*iptyp,ipnit,ipstep,maxdis*
This command controls iterative subspace interpolation. *iptyp* can be:

`DIIS`
- direct inversion of the iterative subspace. This is the default and usually yields
fast and stable convergence.
`KAIN`
- Krylov-subspace accelerated inexact newton. A method similar to DIIS.
`NONE`
- No interpolation.

is the number of the iteration in which the interpolation starts (default: as soon as possible). *ipstep* is the iteration increment between interpolations (default: 1, i.e., every iteration). *maxdis* is
the maximum dimension of the DIIS matrix (default 10). *iptyp* and *maxdis*
can also be set as options. E.g.,
`{rhf,maxdis=20,iptyp='DIIS'; shift,-1.0,-0.5}`

molpro@molpro.net 2017-04-24