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DPPTRF(3F)							    DPPTRF(3F)


NAME    [Toc]    [Back]

     DPPTRF - compute the Cholesky factorization of a real symmetric positive
     definite matrix A stored in packed	format

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	DPPTRF(	UPLO, N, AP, INFO )

	 CHARACTER	UPLO

	 INTEGER	INFO, N

	 DOUBLE		PRECISION AP( *	)

PURPOSE    [Toc]    [Back]

     DPPTRF computes the Cholesky factorization	of a real symmetric positive
     definite matrix A stored in packed	format.

     The factorization has the form
	A = U**T * U,  if UPLO = 'U', or
	A = L  * L**T,	if UPLO	= 'L',
     where U is	an upper triangular matrix and L is lower triangular.

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.

     AP	     (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
	     On	entry, the upper or lower triangle of the symmetric matrix A,
	     packed columnwise in a linear array.  The j-th column of A	is
	     stored in the array AP as follows:	 if UPLO = 'U',	AP(i + (j1)*j/2)
 = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2nj)/2)
 = A(i,j) for	j<=i<=n.  See below for	further	details.

	     On	exit, if INFO =	0, the triangular factor U or L	from the
	     Cholesky factorization A =	U**T*U or A = L*L**T, in the same
	     storage format as A.

     INFO    (output) INTEGER
	     = 0:  successful exit
	     < 0:  if INFO = -i, the i-th argument had an illegal value
	     > 0:  if INFO = i,	the leading minor of order i is	not positive
	     definite, and the factorization could not be completed.

FURTHER	DETAILS
     The packed	storage	scheme is illustrated by the following example when N
     = 4, UPLO = 'U':




									Page 1






DPPTRF(3F)							    DPPTRF(3F)



     Two-dimensional storage of	the symmetric matrix A:

	a11 a12	a13 a14
	    a22	a23 a24
		a33 a34	    (aij = aji)
		    a44

     Packed storage of the upper triangle of A:

     AP	= [ a11, a12, a22, a13,	a23, a33, a14, a24, a34, a44 ]
DPPTRF(3F)							    DPPTRF(3F)


NAME    [Toc]    [Back]

     DPPTRF - compute the Cholesky factorization of a real symmetric positive
     definite matrix A stored in packed	format

SYNOPSIS    [Toc]    [Back]

     SUBROUTINE	DPPTRF(	UPLO, N, AP, INFO )

	 CHARACTER	UPLO

	 INTEGER	INFO, N

	 DOUBLE		PRECISION AP( *	)

PURPOSE    [Toc]    [Back]

     DPPTRF computes the Cholesky factorization	of a real symmetric positive
     definite matrix A stored in packed	format.

     The factorization has the form
	A = U**T * U,  if UPLO = 'U', or
	A = L  * L**T,	if UPLO	= 'L',
     where U is	an upper triangular matrix and L is lower triangular.

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.

     AP	     (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
	     On	entry, the upper or lower triangle of the symmetric matrix A,
	     packed columnwise in a linear array.  The j-th column of A	is
	     stored in the array AP as follows:	 if UPLO = 'U',	AP(i + (j1)*j/2)
 = A(i,j) for 1<=i<=j; if UPLO = 'L', AP(i + (j-1)*(2nj)/2)
 = A(i,j) for	j<=i<=n.  See below for	further	details.

	     On	exit, if INFO =	0, the triangular factor U or L	from the
	     Cholesky factorization A =	U**T*U or A = L*L**T, in the same
	     storage format as A.

     INFO    (output) INTEGER
	     = 0:  successful exit
	     < 0:  if INFO = -i, the i-th argument had an illegal value
	     > 0:  if INFO = i,	the leading minor of order i is	not positive
	     definite, and the factorization could not be completed.

FURTHER	DETAILS
     The packed	storage	scheme is illustrated by the following example when N
     = 4, UPLO = 'U':




									Page 1






DPPTRF(3F)							    DPPTRF(3F)



     Two-dimensional storage of	the symmetric matrix A:

	a11 a12	a13 a14
	    a22	a23 a24
		a33 a34	    (aij = aji)
		    a44

     Packed storage of the upper triangle of A:

     AP	= [ a11, a12, a22, a13,	a23, a33, a14, a24, a34, a44 ]


									PPPPaaaaggggeeee 2222
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