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## ssytrf_aa()

subroutine ssytrf_aa | ( | character | uplo,
|  | integer | n,
|  | real, dimension( lda, * ) | a,
|  | integer | lda,
|  | integer, dimension( * ) | ipiv,
|  | real, dimension( * ) | work,
|  | integer | lwork,
|  | integer | info )

SSYTRF_AA

Download SSYTRF_AA + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> SSYTRF_AA computes the factorization of a real symmetric matrix A
      !> using the Aasen's algorithm.  The form of the factorization is
      !>
      !>    A = U**T*T*U  or  A = L*T*L**T
      !>
      !> where U (or L) is a product of permutation and unit upper (lower)
      !> triangular matrices, and T is a symmetric tridiagonal matrix.
      !>
      !> This is the blocked version of the algorithm, calling Level 3 BLAS.
      !>

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 REAL array, dimension (LDA,N)
      !>          On entry, the symmetric 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, the tridiagonal matrix is stored in the diagonals
      !>          and the subdiagonals of A just below (or above) the diagonals,
      !>          and L is stored below (or above) the subdiagonals, when UPLO
      !>          is 'L' (or 'U').
      !>

  [in]

  LDA

      !>          LDA is INTEGER
      !>          The leading dimension of the array A.  LDA >= max(1,N).
      !>

  [out]

  IPIV

      !>          IPIV is INTEGER array, dimension (N)
      !>          On exit, it contains the details of the interchanges, i.e.,
      !>          the row and column k of A were interchanged with the
      !>          row and column IPIV(k).
      !>

  [out]

  WORK

      !>          WORK is REAL array, dimension (MAX(1,LWORK))
      !>          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
      !>

  [in]

  LWORK

      !>          LWORK is INTEGER
      !>          The length of WORK.
      !>          LWORK >= 1, if N <= 1, and LWORK >= 2*N, otherwise.
      !>          For optimum performance LWORK >= N*(1+NB), where NB is
      !>          the optimal blocksize, returned by ILAENV.
      !>
      !>          If LWORK = -1, then a workspace query is assumed; the routine
      !>          only calculates the optimal size of the WORK array, returns
      !>          this value as the first entry of the WORK array, and no error
      !>          message related to LWORK is issued by XERBLA.
      !>

  [out]

  INFO

      !>          INFO is INTEGER
      !>          = 0:  successful exit
      !>          < 0:  if INFO = -i, the i-th argument had an illegal value.
      !>

Author
  Univ. of Tennessee
  Univ. of California Berkeley
  Univ. of Colorado Denver
  NAG Ltd.