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 consistent 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.