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<h3 class="sectionHead"><span class="titlemark"><span
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class="cmbx-12">7 </span></span> <a
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id="x29-330007"></a><span
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class="cmbx-12">Adding new smoother and solver objects to AMG4PSBLAS</span></h3>
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<!--l. 6--><p class="noindent" ><span
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class="cmbx-12">Developers can add completely new smoother and/or solver classes derived</span>
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<span
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class="cmbx-12">from the base objects in the library (see Remark</span><span
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class="cmbx-12"> 2 in Section</span><span
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class="cmbx-12"> </span><a
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href="userhtmlsu11.html#x21-200006.2"><span
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class="cmbx-12">6.2</span><!--tex4ht:ref: sec:precset --></a><span
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class="cmbx-12">), without</span>
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<span
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class="cmbx-12">recompiling the library itself.</span>
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<!--l. 10--><p class="indent" > <span
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class="cmbx-12">To do so, it is necessary first to select the base type to be extended. In</span>
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<span
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class="cmbx-12">our experience, it is quite likely that the new application needs only the</span>
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<span
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class="cmbx-12">definition of a “solver” object, which is almost always acting only on the</span>
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<span
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class="cmbx-12">local part of the distributed matrix. The parallel actions required to</span>
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<span
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class="cmbx-12">connect the various solver objects are most often already provided by the</span>
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<span
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class="cmbx-12">block-Jacobi or the additive Schwarz smoothers. To define a new solver, the</span>
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<span
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class="cmbx-12">developer will then have to define its components and methods,</span>
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<span
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class="cmbx-12">perhaps taking one of the predefined solvers as a starting point, if</span>
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<span
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class="cmbx-12">possible.</span>
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<!--l. 20--><p class="indent" > <span
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class="cmbx-12">Once the new smoother/solver class has been developed, to use</span>
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<span
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class="cmbx-12">it in the context of the multilevel preconditioners it is necessary</span>
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<span
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class="cmbx-12">to:</span>
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<ul class="itemize1">
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<li class="itemize"><span
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class="cmbx-12">declare in the application program a variable of the new type;</span>
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</li>
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<li class="itemize"><span
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class="cmbx-12">pass that variable as the argument to the </span><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">set</span></span></span> <span
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class="cmbx-12">routine as in the</span>
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<span
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class="cmbx-12">following:</span>
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<div class="center"
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>
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<!--l. 26--><p class="noindent" >
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<!--l. 27--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">call</span><span
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class="cmtt-12"> p%set(smoother,info</span><span
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class="cmtt-12"> [,ilev,ilmax,pos])</span></span></span><br />
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<span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">call</span><span
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class="cmtt-12"> p%set(solver,info</span><span
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class="cmtt-12"> [,ilev,ilmax,pos])</span></span></span></div>
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</li>
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<li class="itemize"><span
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class="cmbx-12">link the code implementing the various methods into the application</span>
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<span
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class="cmbx-12">executable.</span></li></ul>
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<!--l. 32--><p class="noindent" ><span
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class="cmbx-12">The new solver object is then dynamically included in the preconditioner</span>
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<span
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class="cmbx-12">structure, and acts as a </span><span
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class="cmbxti-10x-x-120">mold </span><span
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class="cmbx-12">to which the preconditioner will conform,</span>
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<span
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class="cmbx-12">even though the AMG4PSBLAS library has not been modified to account</span>
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<span
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class="cmbx-12">for this new development.</span>
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<!--l. 37--><p class="indent" > <span
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class="cmbx-12">It is possible to define new values for the keyword </span><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">WHAT</span></span></span> <span
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class="cmbx-12">in the </span><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">set</span></span></span>
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<span
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class="cmbx-12">routine; if the library code does not recognize a keyword, it passes it down</span>
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<span
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class="cmbx-12">the composition hierarchy (levels containing smoothers containing in turn</span>
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<span
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class="cmbx-12">solvers), so that it can be eventually caught by the new solver. By the</span>
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<span
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class="cmbx-12">same token, any keyword/value pair that does not pertain to a given</span>
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<span
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class="cmbx-12">smoother should be passed down to the contained solver, and any</span>
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<span
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class="cmbx-12">keyword/value pair that does not pertain to a given solver is by default</span>
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<span
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class="cmbx-12">ignored.</span>
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<!--l. 46--><p class="indent" > <span
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class="cmbx-12">An example is provided in the source code distribution under the folder</span>
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<span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">tests/newslv</span></span></span><span
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class="cmbx-12">. In this example we are implementing a new incomplete</span>
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<span
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class="cmbx-12">factorization variant (which is simply the ILU(0) factorization under a new</span>
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<span
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class="cmbx-12">name). Because of the specifics of this case, it is possible to reuse the basic</span>
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<span
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class="cmbx-12">structure of the ILU solver, with its L/D/U components and the</span>
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<span
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class="cmbx-12">methods needed to apply the solver; only a few methods, such as the</span>
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<span
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class="cmbx-12">description and most importantly the build, need to be ovverridden</span>
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<span
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class="cmbx-12">(rewritten).</span>
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<!--l. 55--><p class="indent" > <span
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class="cmbx-12">The interfaces for the calls shown above are defined using</span>
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<div class="center"
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>
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<!--l. 56--><p class="noindent" >
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<div class="tabular"> <table id="TBL-21" class="tabular"
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cellspacing="0" cellpadding="0"
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><colgroup id="TBL-21-1g"><col
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id="TBL-21-1"><col
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id="TBL-21-2"></colgroup><tr
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style="vertical-align:baseline;" id="TBL-21-1-"><td style="white-space:wrap; text-align:left;" id="TBL-21-1-1"
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class="td11"><!--l. 58--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">smoother</span></span></span> </td><td style="white-space:wrap; text-align:left;" id="TBL-21-1-2"
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class="td11"><!--l. 58--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">class(amg_x_base_smoother_type)</span></span></span> </td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-21-2-"><td style="white-space:wrap; text-align:left;" id="TBL-21-2-1"
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class="td11"><!--l. 59--><p class="noindent" > </td><td style="white-space:wrap; text-align:left;" id="TBL-21-2-2"
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class="td11"><!--l. 59--><p class="noindent" ><span
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class="cmbx-12">The user-defined new smoother to be employed in the</span>
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<span
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class="cmbx-12">preconditioner.</span> </td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-21-3-"><td style="white-space:wrap; text-align:left;" id="TBL-21-3-1"
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class="td11"><!--l. 61--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">solver</span></span></span> </td><td style="white-space:wrap; text-align:left;" id="TBL-21-3-2"
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class="td11"><!--l. 61--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">class(amg_x_base_solver_type)</span></span></span> </td>
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</tr><tr
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style="vertical-align:baseline;" id="TBL-21-4-"><td style="white-space:wrap; text-align:left;" id="TBL-21-4-1"
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class="td11"><!--l. 62--><p class="noindent" > </td><td style="white-space:wrap; text-align:left;" id="TBL-21-4-2"
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class="td11"><!--l. 62--><p class="noindent" ><span
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class="cmbx-12">The user-defined new solver to be employed in the</span>
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<span
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class="cmbx-12">preconditioner.</span> </td>
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</tr></table></div></div>
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<!--l. 66--><p class="noindent" ><span
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class="cmbx-12">The other arguments are defined in the way described in Sec.</span><span
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class="cmbx-12"> </span><a
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href="userhtmlsu11.html#x21-200006.2"><span
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class="cmbx-12">6.2</span><!--tex4ht:ref: sec:precset --></a><span
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class="cmbx-12">. As an</span>
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<span
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class="cmbx-12">example, in the </span><span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">tests/newslv</span></span></span> <span
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class="cmbx-12">code we define a new object of type</span>
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<span class="obeylines-h"><span class="verb"><span
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class="cmtt-12">amg_d_tlu_solver_type</span></span></span><span
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class="cmbx-12">, and we pass it as follows:</span>
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<div class="verbatim" id="verbatim-10">
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 <br />  ! sparse matrix and preconditioner
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 <br />  type(psb_dspmat_type) :: a
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 <br />  type(amg_dprec_type)  :: prec
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 <br />  type(amg_d_tlu_solver_type) :: tlusv
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 <br />
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 <br />......
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 <br />  !
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 <br />  !  prepare the preconditioner: an ML with defaults, but with TLU solver at
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 <br />  !  intermediate levels. All other parameters are at default values.
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 <br />  !
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 <br />  call prec%init(’ML’,       info)
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 <br />  call prec%hierarchy_build(a,desc_a,info)
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 <br />  nlv = prec%get_nlevs()
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 <br />  call prec%set(tlusv,   info,ilev=1,ilmax=max(1,nlv-1))
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 <br />  call prec%smoothers_build(a,desc_a,info)
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 <br />
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</div>
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<!--l. 88--><p class="nopar" >
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<!--l. 1--><div class="crosslinks"><p class="noindent"><span
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class="cmbx-12">[</span><a
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href="userhtmlse8.html" ><span
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class="cmbx-12">] [</span><a
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href="userhtmlse6.html" ><span
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class="cmbx-12">prev</span></a><span
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class="cmbx-12">] [</span><a
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class="cmbx-12">prev-tail</span></a><span
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class="cmbx-12">] [</span><a
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class="cmbx-12">front</span></a><span
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class="cmbx-12">] [</span><a
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href="userhtml.html#userhtmlse7.html" ><span
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class="cmbx-12">up</span></a><span
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class="cmbx-12">] </span></p></div>
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<!--l. 1--><p class="indent" > <a
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id="tailuserhtmlse7.html"></a>
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