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<!--l. 4--><div class="crosslinks"><p class="noindent"><span
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<h3 class="sectionHead"><span class="titlemark"><span
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class="cmr-12">6 </span></span> <a
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id="x25-290006"></a><span
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class="cmr-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="cmr-12">Developers can add completely new smoother and/or solver classes derived from the</span>
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<span
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class="cmr-12">base objects in the library (see Remark</span><span
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class="cmr-12"> 2 in Section</span><span
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class="cmr-12"> </span><a
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href="userhtmlsu8.html#x17-160005.2"><span
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class="cmr-12">5.2</span><!--tex4ht:ref: sec:precset --></a><span
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class="cmr-12">), without recompiling the</span>
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<span
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class="cmr-12">library itself.</span>
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<!--l. 10--><p class="indent" > <span
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class="cmr-12">To do so, it is necessary first to select the base type to be extended. In our</span>
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<span
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class="cmr-12">experience, it is quite likely that the new application needs only the definition of a</span>
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<span
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class="cmr-12">“solver” object, which is almost always acting only on the local part of the distributed</span>
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<span
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class="cmr-12">matrix. The parallel actions required to connect the various solver objects are most</span>
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<span
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class="cmr-12">often already provided by the block-Jacobi or the additive Schwarz smoothers. To</span>
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<span
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class="cmr-12">define a new solver, the developer will then have to define its components and</span>
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<span
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class="cmr-12">methods, perhaps taking one of the predefined solvers as a starting point, if</span>
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<span
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class="cmr-12">possible.</span>
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<!--l. 20--><p class="indent" > <span
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class="cmr-12">Once the new smoother/solver class has been developed, to use it in the context of</span>
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<span
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class="cmr-12">the multilevel preconditioners it is necessary to:</span>
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<ul class="itemize1">
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<li class="itemize"><span
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class="cmr-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="cmr-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="cmr-12">routine as in the 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="cmr-12">link the code implementing the various methods into the application</span>
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<span
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class="cmr-12">executable.</span></li></ul>
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<!--l. 32--><p class="noindent" ><span
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class="cmr-12">The new solver object is then dynamically included in the preconditioner structure,</span>
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<span
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class="cmr-12">and acts as a </span><span
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class="cmti-12">mold </span><span
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class="cmr-12">to which the preconditioner will conform, even though</span>
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<span
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class="cmr-12">the AMG4PSBLAS library has not been modified to account for this new</span>
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<span
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class="cmr-12">development.</span>
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<!--l. 37--><p class="indent" > <span
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class="cmr-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="cmr-12">in 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="cmr-12">routine; if the</span>
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<span
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class="cmr-12">library code does not recognize a keyword, it passes it down the composition hierarchy</span>
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<span
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class="cmr-12">(levels containing smoothers containing in turn solvers), so that it can be eventually</span>
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<span
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class="cmr-12">caught by the new solver. By the same token, any keyword/value pair that does not</span>
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<span
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class="cmr-12">pertain to a given smoother should be passed down to the contained solver, and</span>
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<span
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class="cmr-12">any 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="cmr-12">ignored.</span>
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<!--l. 46--><p class="indent" > <span
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class="cmr-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="cmr-12">. In this example we are implementing a new incomplete factorization</span>
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<span
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class="cmr-12">variant (which is simply the ILU(0) factorization under a new name). Because of the</span>
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<span
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class="cmr-12">specifics of this case, it is possible to reuse the basic structure of the ILU solver, with</span>
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<span
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class="cmr-12">its L/D/U components and the methods needed to apply the solver; only a few</span>
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<span
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class="cmr-12">methods, such as the description and most importantly the build, need to be</span>
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<span
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class="cmr-12">ovverridden (rewritten).</span>
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<!--l. 55--><p class="indent" > <span
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class="cmr-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="cmr-12">The user-defined new smoother to be employed in the</span>
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<span
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class="cmr-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="cmr-12">The user-defined new solver to be employed in the preconditioner.</span></td></tr></table></div></div>
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<!--l. 66--><p class="noindent" ><span
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class="cmr-12">The other arguments are defined in the way described in Sec.</span><span
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class="cmr-12"> </span><a
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href="userhtmlsu8.html#x17-160005.2"><span
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class="cmr-12">5.2</span><!--tex4ht:ref: sec:precset --></a><span
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class="cmr-12">. As an example, in the</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="cmr-12">code we define a new object of type </span><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="cmr-12">, and we</span>
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<span
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class="cmr-12">pass it as follows:</span>
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<div class="verbatim" id="verbatim-9">
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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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