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<H1><A NAME="SECTION04910000000000000000">Translating BLAS-based programs to the PBLAS</A></H1>
<P>
<A NAME="secApplicationsAndUseOfThePBLAS"> </A>
<A NAME="6785"> </A>
<P>
With a concrete understanding of array descriptors
(Chapter <A HREF="node68.html#chap2dbsd">4</A>), it is relatively simple
to translate the serial version of a BLAS call into its
parallel equivalent. Translating BLAS calls to PBLAS calls primarily
consists of the following steps:
<UL>
<LI> a <TT>`P'</TT> has to be inserted in front of the routine name,
<LI> the leading dimensions should be replaced by the
global <I>array descriptors</I>, and
<LI> the global indices into the distributed matrices should be
inserted as separate parameters in the calling
sequence.
</UL>
An example of translating a DGEMM call to a PDGEMM call is given
below.
<PRE> CALL DGEMM( 'No transpose', 'No transpose', M-J-JB+1, N-J-JB+1,
$ JB, -ONE, A( J+JB, J ), LDA, A( J, J+JB ), LDA, ONE,
$ A( J+JB, J+JB ), LDA )</PRE>
<IMG WIDTH=9 HEIGHT=25 ALIGN=MIDDLE ALT="tex2html_wrap_inline19869" SRC="img749.gif">
<PRE> CALL PDGEMM( 'No transpose', 'No transpose', M-J-JB+JA, N-J-JB+JA,
$ JB, -ONE, A, J+JB, J, DESCA, A, J, J+JB, DESCA, ONE,
$ A, J+JB, J+JB, DESCA )</PRE>
<P>
This simple translation process considerably
simplifies the implementation phase of linear
algebra codes built on top of the BLAS.
<P>
The steps necessary to write a program to call a PBLAS routine
are analogous to the steps presented in section <A HREF="node33.html#basicsteps">2.4</A>.
<P>
<BR> <HR>
<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
</ADDRESS>
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