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SPBSTF(3F)							    SPBSTF(3F)


NAME    [Toc]    [Back]

     SPBSTF - compute a	split Cholesky factorization of	a real symmetric
     positive definite band matrix A

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	SPBSTF(	UPLO, N, KD, AB, LDAB, INFO )

	 CHARACTER	UPLO

	 INTEGER	INFO, KD, LDAB,	N

	 REAL		AB( LDAB, * )

PURPOSE    [Toc]    [Back]

     SPBSTF computes a split Cholesky factorization of a real symmetric
     positive definite band matrix A.

     This routine is designed to be used in conjunction	with SSBGST.

     The factorization has the form  A = S**T*S	 where S is a band matrix of
     the same bandwidth	as A and the following structure:

       S = ( U	  )
	   ( M	L )

     where U is	upper triangular of order m = (n+kd)/2,	and L is lower
     triangular	of order n-m.

ARGUMENTS    [Toc]    [Back]

     UPLO    (input) CHARACTER*1
	     = 'U':  Upper triangle of A is stored;
	     = 'L':  Lower triangle of A is stored.

     N	     (input) INTEGER
	     The order of the matrix A.	 N >= 0.

     KD	     (input) INTEGER
	     The number	of superdiagonals of the matrix	A if UPLO = 'U', or
	     the number	of subdiagonals	if UPLO	= 'L'.	KD >= 0.

     AB	     (input/output) REAL array,	dimension (LDAB,N)
	     On	entry, the upper or lower triangle of the symmetric band
	     matrix A, stored in the first kd+1	rows of	the array.  The	j-th
	     column of A is stored in the j-th column of the array AB as
	     follows:  if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,jkd)<=i<=j;
	if UPLO	= 'L', AB(1+i-j,j)    =	A(i,j) for
	     j<=i<=min(n,j+kd).

	     On	exit, if INFO =	0, the factor S	from the split Cholesky
	     factorization A = S**T*S. See Further Details.  LDAB    (input)
	     INTEGER The leading dimension of the array	AB.  LDAB >= KD+1.



									Page 1






SPBSTF(3F)							    SPBSTF(3F)



     INFO    (output) INTEGER
	     = 0: successful exit
	     < 0: if INFO = -i,	the i-th argument had an illegal value
	     > 0: if INFO = i, the factorization could not be completed,
	     because the updated element a(i,i)	was negative; the matrix A is
	     not positive definite.

FURTHER	DETAILS
     The band storage scheme is	illustrated by the following example, when N =
     7,	KD = 2:

     S = ( s11	s12  s13		     )
	 (	s22  s23  s24		     )
	 (	     s33  s34		     )
	 (		  s44		     )
	 (	     s53  s54  s55	     )
	 (		  s64  s65  s66	     )
	 (		       s75  s76	 s77 )

     If	UPLO = 'U', the	array AB holds:

     on	entry:				on exit:

      *	   *   a13  a24	 a35  a46  a57	 *    *	  s13  s24  s53	 s64  s75
      *	  a12  a23  a34	 a45  a56  a67	 *   s12  s23  s34  s54	 s65  s76 a11
     a22  a33  a44  a55	 a66  a77  s11	s22  s33  s44  s55  s66	 s77

     If	UPLO = 'L', the	array AB holds:

     on	entry:				on exit:

     a11  a22  a33  a44	 a55  a66  a77	s11  s22  s33  s44  s55	 s66  s77 a21
     a32  a43  a54  a65	 a76   *   s12	s23  s34  s54  s65  s76	  * a31	 a42
     a53  a64  a64   *	  *   s13  s24	s53  s64  s75	*    *

     Array elements marked * are not used by the routine.
SPBSTF(3F)							    SPBSTF(3F)


NAME    [Toc]    [Back]

     SPBSTF - compute a	split Cholesky factorization of	a real symmetric
     positive definite band matrix A

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	SPBSTF(	UPLO, N, KD, AB, LDAB, INFO )

	 CHARACTER	UPLO

	 INTEGER	INFO, KD, LDAB,	N

	 REAL		AB( LDAB, * )

PURPOSE    [Toc]    [Back]

     SPBSTF computes a split Cholesky factorization of a real symmetric
     positive definite band matrix A.

     This routine is designed to be used in conjunction	with SSBGST.

     The factorization has the form  A = S**T*S	 where S is a band matrix of
     the same bandwidth	as A and the following structure:

       S = ( U	  )
	   ( M	L )

     where U is	upper triangular of order m = (n+kd)/2,	and L is lower
     triangular	of order n-m.

ARGUMENTS    [Toc]    [Back]

     UPLO    (input) CHARACTER*1
	     = 'U':  Upper triangle of A is stored;
	     = 'L':  Lower triangle of A is stored.

     N	     (input) INTEGER
	     The order of the matrix A.	 N >= 0.

     KD	     (input) INTEGER
	     The number	of superdiagonals of the matrix	A if UPLO = 'U', or
	     the number	of subdiagonals	if UPLO	= 'L'.	KD >= 0.

     AB	     (input/output) REAL array,	dimension (LDAB,N)
	     On	entry, the upper or lower triangle of the symmetric band
	     matrix A, stored in the first kd+1	rows of	the array.  The	j-th
	     column of A is stored in the j-th column of the array AB as
	     follows:  if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,jkd)<=i<=j;
	if UPLO	= 'L', AB(1+i-j,j)    =	A(i,j) for
	     j<=i<=min(n,j+kd).

	     On	exit, if INFO =	0, the factor S	from the split Cholesky
	     factorization A = S**T*S. See Further Details.  LDAB    (input)
	     INTEGER The leading dimension of the array	AB.  LDAB >= KD+1.



									Page 1






SPBSTF(3F)							    SPBSTF(3F)



     INFO    (output) INTEGER
	     = 0: successful exit
	     < 0: if INFO = -i,	the i-th argument had an illegal value
	     > 0: if INFO = i, the factorization could not be completed,
	     because the updated element a(i,i)	was negative; the matrix A is
	     not positive definite.

FURTHER	DETAILS
     The band storage scheme is	illustrated by the following example, when N =
     7,	KD = 2:

     S = ( s11	s12  s13		     )
	 (	s22  s23  s24		     )
	 (	     s33  s34		     )
	 (		  s44		     )
	 (	     s53  s54  s55	     )
	 (		  s64  s65  s66	     )
	 (		       s75  s76	 s77 )

     If	UPLO = 'U', the	array AB holds:

     on	entry:				on exit:

      *	   *   a13  a24	 a35  a46  a57	 *    *	  s13  s24  s53	 s64  s75
      *	  a12  a23  a34	 a45  a56  a67	 *   s12  s23  s34  s54	 s65  s76 a11
     a22  a33  a44  a55	 a66  a77  s11	s22  s33  s44  s55  s66	 s77

     If	UPLO = 'L', the	array AB holds:

     on	entry:				on exit:

     a11  a22  a33  a44	 a55  a66  a77	s11  s22  s33  s44  s55	 s66  s77 a21
     a32  a43  a54  a65	 a76   *   s12	s23  s34  s54  s65  s76	  * a31	 a42
     a53  a64  a64   *	  *   s13  s24	s53  s64  s75	*    *

     Array elements marked * are not used by the routine.


									PPPPaaaaggggeeee 2222
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