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<H2><A NAME="SECTION04231000000000000000">Simplifying Assumptions Used in Example Program</A></H2>
<P>
Several simplifying assumptions and/or restrictions have been made in
this example program in order to present the most basic example for the user:
<UL>
<LI>
We have chosen a small block size, <I>MB</I>=<I>NB</I>=2; however,
this should not be regarded
as a typical choice of block size in a user's application. For best
performance, a choice of <I>MB</I>=<I>NB</I>=32 or <I>MB</I>=<I>NB</I>=64 is more suitable. Refer to
Chapter <A HREF="node104.html#chapperformance">5</A> for further details.
<LI>
A simplistic subroutine MATINIT is used to assign matrices
<I>A</I> and <I>B</I> to the process grid. Note that this subroutine hardcodes
the local arrays on each process and does not perform communication.
It is not a ScaLAPACK routine and is provided only for the purposes
of this example program.
<LI>
We assume <I>RSRC</I>=<I>CSRC</I>=0<A NAME="764"> </A>,
and thus both
matrices <I>A</I> and <I>B</I> are distributed across the process grid starting
with process (0,0). In general, however, any process in the current
process grid can be assigned to receive the first element of the
distributed matrix.
<LI>
We have set the local leading dimension of local array <I>A</I> and the
local leading dimension of local array <I>B</I> to be
the same over all process rows in the process grid.
The variable <I>MXLLDA</I> is equal to the maximum local leading dimension for
array <I>A</I> (denoted <IMG WIDTH=58 HEIGHT=12 ALIGN=BOTTOM ALT="tex2html_wrap_inline12116" SRC="img17.gif">) over all process
rows. Likewise, variable <I>MXLLDB</I> is the maximum local leading dimension for
array <I>B</I> (denoted <IMG WIDTH=58 HEIGHT=12 ALIGN=BOTTOM ALT="tex2html_wrap_inline12120" SRC="img18.gif">) over all process rows. In general, however,
the local leading dimension of the local array can differ from
process to process in the process grid.
<LI>
The system is solved
by using the entire matrix <I>A</I>, as opposed to a submatrix of <I>A</I>, so the global
indices, denoted by <I>IA</I>, <I>JA</I>, <I>IB</I>, and
<I>JB</I><A NAME="765"> </A><A NAME="766"> </A><A NAME="767"> </A><A NAME="768"> </A><A NAME="769"> </A>,
into the matrix are equal to 1. Refer
to figure <A HREF="node79.html#figview">4.7</A> in section <A HREF="node79.html#subsecargdesc">4.3.5</A>
for more information on the representation of global addressing into a
distributed submatrix.
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<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
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