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)) ).

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.

UPLO

          UPLO is CHARACTER*1


          = 'U':  A is upper triangular;


          = 'L':  A is lower triangular.

DIAG

          DIAG is CHARACTER*1


          = 'N':  A is non-unit triangular;


          = 'U':  A is unit triangular.

N

          N is INTEGER


          The order of the matrix A.  N >= 0.

KD

          KD is INTEGER


          The number of superdiagonals or subdiagonals of the


          triangular band matrix A.  KD >= 0.

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.

LDAB

          LDAB is INTEGER


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

RCOND

          RCOND is DOUBLE PRECISION


          The reciprocal of the condition number of the matrix A,


          computed as RCOND = 1/(norm(A) * norm(inv(A))).

WORK

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

IWORK

          IWORK is INTEGER array, dimension (N)

INFO

          INFO is INTEGER


          = 0:  successful exit


          < 0:  if INFO = -i, the i-th argument had an illegal value

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

November 2011