dlangt(3F)

NAME
     DLANGT - return the value of the one norm, or the Frobenius norm, or the
     infinity norm, or the element of largest absolute value of a real
     tridiagonal matrix A

SYNOPSIS
     DOUBLE PRECISION FUNCTION DLANGT( NORM, N, DL, D, DU )

         CHARACTER    NORM

         INTEGER      N

         DOUBLE       PRECISION D( * ), DL( * ), DU( * )

PURPOSE
     DLANGT  returns the value of the one norm,  or the Frobenius norm, or the
     infinity norm,  or the  element of  largest absolute value  of a real
     tridiagonal matrix A.


DESCRIPTION
     DLANGT returns the value

        DLANGT = ( max(abs(A(i,j))), NORM = 'M' or 'm'
                 (
                 ( norm1(A),         NORM = '1', 'O' or 'o'
                 (
                 ( normI(A),         NORM = 'I' or 'i'
                 (
                 ( normF(A),         NORM = 'F', 'f', 'E' or 'e'

     where  norm1  denotes the  one norm of a matrix (maximum column sum),
     normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
     normF  denotes the  Frobenius norm of a matrix (square root of sum of
     squares).  Note that  max(abs(A(i,j)))  is not a  matrix norm.


ARGUMENTS
     NORM    (input) CHARACTER*1
             Specifies the value to be returned in DLANGT as described above.

     N       (input) INTEGER
             The order of the matrix A.  N >= 0.  When N = 0, DLANGT is set to
             zero.

     DL      (input) DOUBLE PRECISION array, dimension (N-1)
             The (n-1) sub-diagonal elements of A.

     D       (input) DOUBLE PRECISION array, dimension (N)
             The diagonal elements of A.
     DU      (input) DOUBLE PRECISION array, dimension (N-1)
             The (n-1) super-diagonal elements of A.