amg4psblas/README

                         MLD2P4  version 2.1
MultiLevel Domain Decomposition Parallel Preconditioners Package
           based on PSBLAS (Parallel Sparse BLAS version 3.5)
    
Salvatore Filippone    Cranfield University, UK
Pasqua D'Ambra         IAC-CNR, Naples, IT
Daniela di Serafino    Univ. of Campania "L. Vanvitelli", Caserta, IT

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MLD2P4 (MultiLevel Domain Decomposition Parallel Preconditioners
Package based on PSBLAS) provides parallel Algebraic MultiGrid (AMG)
and Domain Decomposition preconditioners, to be used in the
iterative solution of linear systems.

The name of the package comes from its original implementation,
containing multilevel additive and hybrid Schwarz preconditioners,
as well as one-level additive Schwarz preconditioners. The current
version extends the original plan by including multilevel cycles
and smoothers widely used in multigrid methods. A purely algebraic
approach is applied to generate coarse-level corrections, so that
no geometric background is needed concerning the matrix to be
preconditioned.

MLD2P4 has been designed to provide scalable and easy-to-use 
preconditioners in the context of the PSBLAS (Parallel Sparse Basic
Linear Algebra Subprograms) computational framework and is used
in conjuction with the Krylov solvers available from PSBLAS. The
package employs object-oriented design techniques in Fortran 2003,
with interfaces to additional third party libraries such as MUMPS,
UMFPACK, SuperLU, and SuperLU_Dist, which can be exploited in building
multilevel preconditioners. The parallel implementation is based on
a Single Program Multiple Data (SPMD) paradigm; the inter-process
communication is based on MPI and is managed mainly through PSBLAS.


Main reference:

   P. D'Ambra, D. di Serafino, S. Filippone,
   MLD2P4: a Package of Parallel Algebraic Multilevel Domain
   Decomposition Preconditioners in Fortran 95,
   ACM Transactions on Mathematical Software, 37 (3), 2010, art. 30,
   doi: 10.1145/1824801.1824808.


WHAT'S NEW

Version 2.1
   1. The multigrid preconditioner now include fully general V- and
      W-cycles. We also support K-cycles, both for symmetric and 
      nonsymmetric matrices, intended to be used in conjunction 
      with Flexible CG or GCR available in PSBLAS 3.5.
   2. The smoothers now include popular variants such as Jacobi,
      forward and backward hybrid Gauss-Seidel (intra-process
      Gauss-Seidel, inter-process block-Jacobi).
   3. The PRE and POST specification for smoothers can now be 
      specified independently of each other: you can even specify
      different  smoothers for PRE and POST (e.g. forward Gauss-Seidel
      PRE with backward Gauss-Seidel POST). The default is to
      have the specs apply to both PRE and POST. 

Version 2.0.

   Finally moved to F2003, with the support of PSBLAS3.
   There are a few minor differences at user level: 
   1. In the configure step, you should specify the INSTALL directory
      of PSBLAS version 3.4, not the source directory;
   2. In the various makefiles, libmld_prec.a should now be used in
      addition (and in front of) libpsb_prec.a, and no longer in
      place of it.
   3. As for the basic usage, this is practically identical to the
      previous version(s).  
   
   You should use the same MPI/serial compilers that were used for the
   PSBLAS installation. 
   The Fortran 2003 support means that it is far easier to develop and
   integrate new solvers and smoothers; you need to take one of the
   existing solvers/smoothers as a model, develop your own by
   changing/replacing the model contents, and then pass the new object
   to the PREC%SET() method which will copy into the internals, as per
   the PROTOTYPE design pattern. Take a look at the test/newslv
   directory to see an example. It's easier done than said!

   Versions known to work: 
   UMFPACK:      5.4
   SuperLU:      4.3 and 5.0
   SuperLU_Dist: 3.3 and 4.2
   Note that with SuperLU_Dist you will probably need to add further
   link options, e.g. the ParMetis library or the openmp runtime;
   you can do this using the configure option --with-extra-libs

In version 1.1:
-  The MLD_SIZEOF() function has been redefined to be INTEGER(8), so
   as to be able to measure large data sets.
-  The internals of the multilevel preconditioner have been repackaged
   in a more structured fashion; no changes are needed in the user
   code.
-  Note that we now need version 2.3.1 of PSBLAS.
   

TO COMPILE

0. Unpack the tar file in a directory of your choice (preferrably
   outside the main PSBLAS directory).
1. run configure --with-psblas=<ABSOLUTE path of the PSBLAS install directory>
   adding the options for SuperLU, SuperLU_Dist, UMFPACK as desired.
   See MLD2P4 User's and Reference Guide (Section 3) for details.
2. Tweak Make.inc if you are not satisfied.
3. make; 
4. Go into the test subdirectory and build the examples of your choice.


NOTES

- The single precision version is  supported only by SuperLU; thus, even
  if you specify at configure to use UMFPACK or SuperLU_Dist, the
  corresponding preconditioner options will be available only from the
  double precision version.

- A program that was using the PSBLAS precoditioners needs no source
  code changes, but should be recompiled. If the new preconditioner
  (or preconditioner options, such as ILU(N) factorization) are
  required, only the type of the preconditioner object and its
  setup/build/free calls should be updated; the rest of the
  application continues to make use of the PSBLAS existing
  interfaces. 


CREDITS

Contributors to version 2:
Salvatore  Filippone 
Pasqua     D'Ambra
Daniela    di Serafino
Ambra	   Abdullahi Hassan


Contributors to version 1:
Salvatore  Filippone 
Pasqua     D'Ambra
Daniela    di Serafino
Alfredo    Buttari