Preconditioners

A preconditioner is defined by

define preconditioner <name> -type=<type> <flaglist>

Example:

define preconditioner c -type=multigrid -bilinearform=a -smoothingsteps=2

A preconditioner must have a type flags specifying the type of preconditioner. The remaining flags depend on the preconditioner.

Preconditioners are:

• -type=local: Local preconditioner, symmetric Gauss-Seidel Jacobi, block Gauss-Seidel

  Flags are

  -bilinearform=<name>	name of bilinear-form containing matrix
  -block	use block Gauss-Seidel (block defined by fe-space)

• -type=multigrid: Multigrid preconditioner

  Flags are

  -bilinearform=<name>	name of bilinear-form containing matrix
  -smoother=<smoother>	type of smoother: 'point'..GS, 'block'..block GS, 'line'..line-GS (lines by anisotropic mesh)
  -coarsetype=<coarse>	type of coarse grid solver: 'exact'..factorization, 'smoothing'..use smoother, 'cg'..inner cg iteration
  -smoothingsteps=nsm	number of pre- and post-smoothing steps
  -increasesmoothingsteps=inc	smoothing steps on level $l$ are $nsm * inc^{L-l}$ with $L$..finest level
  -coarsesmoothingsteps=nsmc	smoothing steps for coarse grid solver (if smoother)
  -finesmoothingsteps=nsmf	smoothing steps for high order equation

• -type=direct: Cholesky factorization