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## dtbcon()

subroutine dtbcon | ( | character | norm,
|  | character | uplo,
|  | character | diag,
|  | integer | n,
|  | integer | kd,
|  | double precision, dimension( ldab, * ) | ab,
|  | integer | ldab,
|  | double precision | rcond,
|  | double precision, dimension( * ) | work,
|  | integer, dimension( * ) | iwork,
|  | integer | info )

DTBCON

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

Purpose:

      !>
      !> DTBCON estimates the reciprocal of the condition number of a
      !> triangular band matrix A, in either the 1-norm or the infinity-norm.
      !>
      !> The norm of A is computed and an estimate is obtained for
      !> norm(inv(A)), then the reciprocal of the condition number is
      !> computed as
      !>    RCOND = 1 / ( norm(A) * norm(inv(A)) ).
      !>

Parameters

  [in]

  NORM

      !>          NORM is CHARACTER*1
      !>          Specifies whether the 1-norm condition number or the
      !>          infinity-norm condition number is required:
      !>          = '1' or 'O':  1-norm;
      !>          = 'I':         Infinity-norm.
      !>

  [in]

  UPLO

      !>          UPLO is CHARACTER*1
      !>          = 'U':  A is upper triangular;
      !>          = 'L':  A is lower triangular.
      !>

  [in]

  DIAG

      !>          DIAG is CHARACTER*1
      !>          = 'N':  A is non-unit triangular;
      !>          = 'U':  A is unit triangular.
      !>

  [in]

  N

      !>          N is INTEGER
      !>          The order of the matrix A.  N >= 0.
      !>

  [in]

  KD

      !>          KD is INTEGER
      !>          The number of superdiagonals or subdiagonals of the
      !>          triangular band matrix A.  KD >= 0.
      !>

  [in]

  AB

      !>          AB is DOUBLE PRECISION array, dimension (LDAB,N)
      !>          The upper or lower triangular 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,j-kd)<=i<=j;
      !>          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd).
      !>          If DIAG = 'U', the diagonal elements of A are not referenced
      !>          and are assumed to be 1.
      !>

  [in]

  LDAB

      !>          LDAB is INTEGER
      !>          The leading dimension of the array AB.  LDAB >= KD+1.
      !>

  [out]

  RCOND

      !>          RCOND is DOUBLE PRECISION
      !>          The reciprocal of the condition number of the matrix A,
      !>          computed as RCOND = 1/(norm(A) * norm(inv(A))).
      !>

  [out]

  WORK

      !>          WORK is DOUBLE PRECISION array, dimension (3*N)
      !>

  [out]

  IWORK

      !>          IWORK is INTEGER array, dimension (N)
      !>

  [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.