zpotrf2()

recursive subroutine zpotrf2	(	character	uplo,
		integer	n,
		complex*16, dimension( lda, * )	a,
		integer	lda,
		integer	info )

ZPOTRF2

Purpose:

!>
!> ZPOTRF2 computes the Cholesky factorization of a Hermitian
!> positive definite matrix A using the recursive algorithm.
!>
!> The factorization has the form
!>    A = U**H * U,  if UPLO = 'U', or
!>    A = L  * L**H,  if UPLO = 'L',
!> where U is an upper triangular matrix and L is lower triangular.
!>
!> This is the recursive version of the algorithm. It divides
!> the matrix into four submatrices:
!>
!>        [  A11 | A12  ]  where A11 is n1 by n1 and A22 is n2 by n2
!>    A = [ -----|----- ]  with n1 = n/2
!>        [  A21 | A22  ]       n2 = n-n1
!>
!> The subroutine calls itself to factor A11. Update and scale A21
!> or A12, update A22 then call itself to factor A22.
!>
!> 

Parameters

[in]	UPLO	!> UPLO is CHARACTER*1 !> = 'U': Upper triangle of A is stored; !> = 'L': Lower triangle of A is stored. !>
[in]	N	!> N is INTEGER !> The order of the matrix A. N >= 0. !>
[in,out]	A	!> A is COMPLEX*16 array, dimension (LDA,N) !> On entry, the Hermitian matrix A. If UPLO = 'U', the leading !> N-by-N upper triangular part of A contains the upper !> triangular part of the matrix A, and the strictly lower !> triangular part of A is not referenced. If UPLO = 'L', the !> leading N-by-N lower triangular part of A contains the lower !> triangular part of the matrix A, and the strictly upper !> triangular part of A is not referenced. !> !> On exit, if INFO = 0, the factor U or L from the Cholesky !> factorization A = U**H*U or A = L*L**H. !>
[in]	LDA	!> LDA is INTEGER !> The leading dimension of the array A. LDA >= max(1,N). !>
[out]	INFO	!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -i, the i-th argument had an illegal value !> > 0: if INFO = i, the leading principal minor of order i !> is not positive, and the factorization could not be !> completed. !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.