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<H2><A NAME="SECTION04922000000000000000">Parallel LU Factorization</A></H2>
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<A NAME="secParallelLUFactorization"> </A>
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<PRE> SUBROUTINE PDGETRF( M, N, A, IA, JA, DESCA, IPIV, INFO )
*
INTEGER IA, INFO, JA, M, N, DESCA( * ), IPIV( * )
DOUBLE PRECISION A( * )
*
* LU factorization of a M-by-N distributed matrix A(IA:IA+M-1,JA:JA+N-1)
* using partial pivoting with row interchanges.
*
INTEGER I, IINFO, J, JB
EXTERNAL IGAMN2D, PDGEMM, PDGETF2, PDLASWP, PDTRSM
INTRINSIC MIN
*
DO 10 J = JA, JA+MIN(M,N)-1, DESCA( NB_ )
JB = MIN( MIN(M,N)-J+JA, DESCA( NB_ ) )
I = IA + J - JA
*
* Factor diagonal block and test for exact singularity.
*
CALL PDGETF2( M-J+JA, JB, A, I, J, DESCA, IPIV, IINFO )
IF( INFO.EQ.0 .AND. IINFO.GT.0 ) INFO = IINFO + J - JA
*
* Apply interchanges to columns JA:J-JA and J+JB:JA+N-1.
*
CALL PDLASWP( 'Forward', 'Rows', J-JA, A, IA, JA, DESCA,
$ I, I+JB-1, IPIV )
IF( J-JA+JB+1.LE.N ) THEN
CALL PDLASWP( 'Forward', 'Rows', N-J-JB+JA, A, IA, J+JB,
$ DESCA, I, I+JB-1, IPIV )
*
* Compute block row of U and update trailing submatrix.
*
CALL PDTRSM( 'Left', 'Lower', 'No transpose', 'Unit', JB,
$ N-J-JB+JA, 1.0D+0, A, I, J, DESCA, A, I, J+JB,
$ DESCA )
IF( J-JA+JB+1.LE.M ) THEN
$ CALL PDGEMM( 'No transpose', 'No transpose', M-J-JB+JA,
$ N-J-JB+JA, JB, -1.0D+0, A, I+JB, J, DESCA, A,
$ I, J+JB, DESCA, 1.0D+0, A, I+JB, J+JB, DESCA )
END IF
10 CONTINUE
IF( INFO.EQ.0 ) INFO = MIN(M,N) + 1
CALL IGAMN2D( ICTXT, 'Row', ' ', 1, 1, INFO, 1, I, J, -1, -1, MYCOL )
IF( INFO.EQ.MIN(M,N)+1 ) INFO = 0
*
RETURN
*
END</PRE>
<P>
The required steps to call a ScaLAPACK routine from a parallel
program are demonstrated in Example Program #1 in Chapter <A HREF="node25.html#howto">2</A>
and explained in section <A HREF="node28.html#example1">2.3</A>.
<P>
<BR> <HR>
<P><ADDRESS>
<I>Susan Blackford <BR>
Tue May 13 09:21:01 EDT 1997</I>
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