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<H1><A NAME="SECTION00090000000000000000"></A><A NAME="sec:adding"></A>
<BR>
Adding new smoothers and solvers to MLD2P4
</H1>
<P>
Developers can add completely new smoother and/or solver classes
derived from the base objects in the library may be used without
recompiling the library itself.
<P>
To do so it is necessary first to select the base type to be extended;
in our experience, it is quite likely that the new application needs
only require the definition of a ``solver'' object, which is almost
always acting only on the local part of the distributed matrix.
<P>
The parallel actions required to connect the various solver objects
are most often already provided by the Block Jacobi or the Additive
Schwarz smoothers. To define a new solver, the developer will then
have to define its components and methods, perhaps taking one of the
predefined solvers as a starting point if possible.
<P>
Once the new smoother/solver class has been developed, to use it in
the context of the multilevel preconditioners it is necessary to:
<UL>
<LI>Declare in the application program a variable of the new type;
</LI>
<LI>Pass that variable as the argument to the se routine as in the
following:
<DIV ALIGN="CENTER">
<code>call p%set(smoother,info [,ilev, ilmax,pos])</code>
<BR><code>call p%set(solver,info [,ilev, ilmax,pos])</code>
</DIV>
</LI>
<LI>Link into the application executable the code implementing the
various methods.
</LI>
</UL>
The new solver object is then dynamically included in the
preconditioner structure, and will act as a <I>mold</I> to which the
preconditioner will conform, even though the MLD2P4 library has not
been modified to account for this new development.
<P>
It is possible to define new values for the keyword <code>WHAT</code> in the
<code>set</code> routines; if the library code does not recognize a keyword,
it passes it down the composition hierarchy (levels containing
smoothers containing solvers), so that it can be eventually caught by
the new solver.
<P>
An example is contained in the source code distribution under the
folder <code>tests/newslv</code>. This example solver is simply the ILU(0)
solver under a new name, but it should give an idea of what needs to
be done.
<P>
<BR>
<P>
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>smoother</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><code>class(mld_x_base_smoother_type)</code></TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34> </TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>The user-defined new smoother to be employed in the
preconditioner.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>solver</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><code>class(mld_x_base_solver_type)</code></TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34> </TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>The user-defined new solver to be employed in the
preconditioner.</TD>
</TR>
</TABLE>
<P>
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