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<H2><A NAME="SECTION00084000000000000000"></A><A NAME="sec:precaply"></A>
<BR>
Subroutine mld_precaply
</H2>

<P>
<DIV ALIGN="CENTER">
<code>mld_precaply(p,x,y,desc_a,info)</code>
<BR><code>mld_precaply(p,x,y,desc_a,info,trans,work)</code>
<BR>
</DIV>

<P>
This routine computes <!-- MATH
 $y = op(M^{-1})\, x$
 -->
<IMG
 WIDTH="117" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
 SRC="img96.png"
 ALT="$y = op(M^{-1})  x$">, where <IMG
 WIDTH="23" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
 SRC="img59.png"
 ALT="$M$"> is a previously built
preconditioner, stored into <code>p</code>, and <IMG
 WIDTH="22" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
 SRC="img97.png"
 ALT="$op$">
denotes the preconditioner itself or its transpose, according to
the value of <code>trans</code>.
Note that, when MLD2P4 is used with a Krylov solver from PSBLAS,
<code>mld_precaply</code> is called within the PSBLAS routine <code>psb_krylov</code>
and hence it is completely transparent to the user.

<P>
<FONT SIZE="+1"><B>Arguments</B></FONT>

<P>
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>p</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><code>type(mld_</code><I>x</I><code>prec_type), intent(inout)</code>.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>The preconditioner data structure, containing the local part of <IMG
 WIDTH="23" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
 SRC="img59.png"
 ALT="$M$">.
                Note that <I>x</I> must be chosen according
                to the real/complex, single/double precision version of MLD2P4 under use.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>x</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><I>type</I><code>(</code><I>kind_parameter</I><code>), dimension(:), intent(in)</code>.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>The local part of the vector <IMG
 WIDTH="14" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
 SRC="img98.png"
 ALT="$x$">. Note that <I>type</I> and   
                <I>kind_parameter</I> must be chosen according
                to the real/complex, single/double precision version of MLD2P4 under use.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>y</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><I>type</I><code>(</code><I>kind_parameter</I><code>), dimension(:), intent(out)</code>.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>The local part of the vector <IMG
 WIDTH="14" HEIGHT="31" ALIGN="MIDDLE" BORDER="0"
 SRC="img99.png"
 ALT="$y$">. Note that <I>type</I> and
                <I>kind_parameter</I> must be chosen according
                to the real/complex, single/double precision version of MLD2P4 under use.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>desc_a</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><code>type(psb_desc_type), intent(in)</code>.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>The communication descriptor associated to the matrix to be
                preconditioned.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>info</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><code>integer, intent(out)</code>.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>Error code. If no error, 0 is returned. See Section&nbsp;<A HREF="node23.html#sec:errors">7</A> for details.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>trans</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><code>character(len=1), optional, intent(in).</code></TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>If <code>trans</code> = <code>'N','n'</code> then <!-- MATH
 $op(M^{-1}) = M^{-1}$
 -->
<IMG
 WIDTH="132" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
 SRC="img100.png"
 ALT="$op(M^{-1}) = M^{-1}$">;
                if <code>trans</code> = <code>'T','t'</code> then <!-- MATH
 $op(M^{-1}) = M^{-T}$
 -->
<IMG
 WIDTH="135" HEIGHT="40" ALIGN="MIDDLE" BORDER="0"
 SRC="img101.png"
 ALT="$op(M^{-1}) = M^{-T}$">
                (transpose of <IMG
 WIDTH="48" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
 SRC="img102.png"
 ALT="$M^{-1})$">;  if <code>trans</code> = <code>'C','c'</code> then <!-- MATH
 $op(M^{-1}) = M^{-C}$
 -->
<IMG
 WIDTH="136" HEIGHT="40" ALIGN="MIDDLE" BORDER="0"
 SRC="img103.png"
 ALT="$op(M^{-1}) = M^{-C}$">
                (conjugate transpose of <IMG
 WIDTH="48" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
 SRC="img102.png"
 ALT="$M^{-1})$">.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34><code>work</code></TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340><I>type</I><code>(</code><I>kind_parameter</I><code>), dimension(:), optional, target</code>.</TD>
</TR>
<TR><TD ALIGN="LEFT" VALIGN="TOP" WIDTH=34>&nbsp;</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=340>Workspace. Its size should be at
               least <code>4 * psb_cd_get_local_</code> <code>cols(desc_a)</code> (see the PSBLAS User's Guide).
               Note that <I>type</I> and <I>kind_parameter</I> must be chosen according
               to the real/complex, single/double precision version of MLD2P4 under use.</TD>
</TR>
</TABLE>

<P>

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