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