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<h3 class="sectionHead"><span class="titlemark"><span
class="cmr-12">6 </span></span> <a
id="x25-290006"></a><span
class="cmr-12">Adding new smoother and solver objects to AMG4PSBLAS</span></h3>
<!--l. 6--><p class="noindent" ><span
class="cmr-12">Developers can add completely new smoother and/or solver classes derived from the</span>
<span
class="cmr-12">base objects in the library (see Remark</span><span
class="cmr-12">&#x00A0;2 in Section</span><span
class="cmr-12">&#x00A0;</span><a
href="userhtmlsu8.html#x17-160005.2"><span
class="cmr-12">5.2</span><!--tex4ht:ref: sec:precset --></a><span
class="cmr-12">), without recompiling the</span>
<span
class="cmr-12">library itself.</span>
<!--l. 10--><p class="indent" > <span
class="cmr-12">To do so, it is necessary first to select the base type to be extended. In our</span>
<span
class="cmr-12">experience, it is quite likely that the new application needs only the definition of a</span>
<span
class="cmr-12">&#8220;solver&#8221; object, which is almost always acting only on the local part of the distributed</span>
<span
class="cmr-12">matrix. The parallel actions required to connect the various solver objects are most</span>
<span
class="cmr-12">often already provided by the block-Jacobi or the additive Schwarz smoothers. To</span>
<span
class="cmr-12">define a new solver, the developer will then have to define its components and</span>
<span
class="cmr-12">methods, perhaps taking one of the predefined solvers as a starting point, if</span>
<span
class="cmr-12">possible.</span>
<!--l. 20--><p class="indent" > <span
class="cmr-12">Once the new smoother/solver class has been developed, to use it in the context of</span>
<span
class="cmr-12">the multilevel preconditioners it is necessary to:</span>
<ul class="itemize1">
<li class="itemize"><span
class="cmr-12">declare in the application program a variable of the new type;</span>
</li>
<li class="itemize"><span
class="cmr-12">pass that variable as the argument to the </span><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">set</span></span></span> <span
class="cmr-12">routine as in the following:</span>
<div class="center"
>
<!--l. 26--><p class="noindent" >
<!--l. 27--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">call</span><span
class="cmtt-12">&#x00A0;p%set(smoother,info</span><span
class="cmtt-12">&#x00A0;[,ilev,ilmax,pos])</span></span></span><br />
<span class="obeylines-h"><span class="verb"><span
class="cmtt-12">call</span><span
class="cmtt-12">&#x00A0;p%set(solver,info</span><span
class="cmtt-12">&#x00A0;[,ilev,ilmax,pos])</span></span></span></div>
</li>
<li class="itemize"><span
class="cmr-12">link the code implementing the various methods into the application</span>
<span
class="cmr-12">executable.</span></li></ul>
<!--l. 32--><p class="noindent" ><span
class="cmr-12">The new solver object is then dynamically included in the preconditioner structure,</span>
<span
class="cmr-12">and acts as a </span><span
class="cmti-12">mold </span><span
class="cmr-12">to which the preconditioner will conform, even though</span>
<span
class="cmr-12">the AMG4PSBLAS library has not been modified to account for this new</span>
<span
class="cmr-12">development.</span>
<!--l. 37--><p class="indent" > <span
class="cmr-12">It is possible to define new values for the keyword </span><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">WHAT</span></span></span> <span
class="cmr-12">in the </span><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">set</span></span></span> <span
class="cmr-12">routine; if the</span>
<span
class="cmr-12">library code does not recognize a keyword, it passes it down the composition hierarchy</span>
<span
class="cmr-12">(levels containing smoothers containing in turn solvers), so that it can be eventually</span>
<span
class="cmr-12">caught by the new solver. By the same token, any keyword/value pair that does not</span>
<span
class="cmr-12">pertain to a given smoother should be passed down to the contained solver, and</span>
<span
class="cmr-12">any keyword/value pair that does not pertain to a given solver is by default</span>
<span
class="cmr-12">ignored.</span>
<!--l. 46--><p class="indent" > <span
class="cmr-12">An example is provided in the source code distribution under the folder</span>
<span class="obeylines-h"><span class="verb"><span
class="cmtt-12">tests/newslv</span></span></span><span
class="cmr-12">. In this example we are implementing a new incomplete factorization</span>
<span
class="cmr-12">variant (which is simply the ILU(0) factorization under a new name). Because of the</span>
<span
class="cmr-12">specifics of this case, it is possible to reuse the basic structure of the ILU solver, with</span>
<span
class="cmr-12">its L/D/U components and the methods needed to apply the solver; only a few</span>
<span
class="cmr-12">methods, such as the description and most importantly the build, need to be</span>
<span
class="cmr-12">ovverridden (rewritten).</span>
<!--l. 55--><p class="indent" > <span
class="cmr-12">The interfaces for the calls shown above are defined using</span>
<div class="center"
>
<!--l. 56--><p class="noindent" >
<div class="tabular"> <table id="TBL-21" class="tabular"
cellspacing="0" cellpadding="0"
><colgroup id="TBL-21-1g"><col
id="TBL-21-1"><col
id="TBL-21-2"></colgroup><tr
style="vertical-align:baseline;" id="TBL-21-1-"><td style="white-space:wrap; text-align:left;" id="TBL-21-1-1"
class="td11"><!--l. 58--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">smoother</span></span></span> </td><td style="white-space:wrap; text-align:left;" id="TBL-21-1-2"
class="td11"><!--l. 58--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">class(amg_x_base_smoother_type)</span></span></span> </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-21-2-"><td style="white-space:wrap; text-align:left;" id="TBL-21-2-1"
class="td11"><!--l. 59--><p class="noindent" > </td><td style="white-space:wrap; text-align:left;" id="TBL-21-2-2"
class="td11"><!--l. 59--><p class="noindent" ><span
class="cmr-12">The user-defined new smoother to be employed in the</span>
<span
class="cmr-12">preconditioner.</span> </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-21-3-"><td style="white-space:wrap; text-align:left;" id="TBL-21-3-1"
class="td11"><!--l. 61--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">solver</span></span></span> </td><td style="white-space:wrap; text-align:left;" id="TBL-21-3-2"
class="td11"><!--l. 61--><p class="noindent" ><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">class(amg_x_base_solver_type)</span></span></span> </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-21-4-"><td style="white-space:wrap; text-align:left;" id="TBL-21-4-1"
class="td11"><!--l. 62--><p class="noindent" > </td><td style="white-space:wrap; text-align:left;" id="TBL-21-4-2"
class="td11"><!--l. 62--><p class="noindent" ><span
class="cmr-12">The user-defined new solver to be employed in the preconditioner.</span></td></tr></table></div></div>
<!--l. 66--><p class="noindent" ><span
class="cmr-12">The other arguments are defined in the way described in Sec.</span><span
class="cmr-12">&#x00A0;</span><a
href="userhtmlsu8.html#x17-160005.2"><span
class="cmr-12">5.2</span><!--tex4ht:ref: sec:precset --></a><span
class="cmr-12">. As an example, in the</span>
<span class="obeylines-h"><span class="verb"><span
class="cmtt-12">tests/newslv</span></span></span> <span
class="cmr-12">code we define a new object of type </span><span class="obeylines-h"><span class="verb"><span
class="cmtt-12">amg_d_tlu_solver_type</span></span></span><span
class="cmr-12">, and we</span>
<span
class="cmr-12">pass it as follows:</span>
<div class="verbatim" id="verbatim-9">
&#x00A0;<br />&#x00A0;&#x00A0;!&#x00A0;sparse&#x00A0;matrix&#x00A0;and&#x00A0;preconditioner
&#x00A0;<br />&#x00A0;&#x00A0;type(psb_dspmat_type)&#x00A0;::&#x00A0;a
&#x00A0;<br />&#x00A0;&#x00A0;type(amg_dprec_type)&#x00A0;&#x00A0;::&#x00A0;prec
&#x00A0;<br />&#x00A0;&#x00A0;type(amg_d_tlu_solver_type)&#x00A0;::&#x00A0;tlusv
&#x00A0;<br />
&#x00A0;<br />......
&#x00A0;<br />&#x00A0;&#x00A0;!
&#x00A0;<br />&#x00A0;&#x00A0;!&#x00A0;&#x00A0;prepare&#x00A0;the&#x00A0;preconditioner:&#x00A0;an&#x00A0;ML&#x00A0;with&#x00A0;defaults,&#x00A0;but&#x00A0;with&#x00A0;TLU&#x00A0;solver&#x00A0;at
&#x00A0;<br />&#x00A0;&#x00A0;!&#x00A0;&#x00A0;intermediate&#x00A0;levels.&#x00A0;All&#x00A0;other&#x00A0;parameters&#x00A0;are&#x00A0;at&#x00A0;default&#x00A0;values.
&#x00A0;<br />&#x00A0;&#x00A0;!
&#x00A0;<br />&#x00A0;&#x00A0;call&#x00A0;prec%init(&#8217;ML&#8217;,&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;&#x00A0;info)
&#x00A0;<br />&#x00A0;&#x00A0;call&#x00A0;prec%hierarchy_build(a,desc_a,info)
&#x00A0;<br />&#x00A0;&#x00A0;nlv&#x00A0;=&#x00A0;prec%get_nlevs()
&#x00A0;<br />&#x00A0;&#x00A0;call&#x00A0;prec%set(tlusv,&#x00A0;&#x00A0;&#x00A0;info,ilev=1,ilmax=max(1,nlv-1))
&#x00A0;<br />&#x00A0;&#x00A0;call&#x00A0;prec%smoothers_build(a,desc_a,info)
&#x00A0;<br />
</div>
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