dlangt(3)

NAME

DLANGT - return the value of the one norm, or the Frobe

nius norm, or the infinity norm, or the element of largest abso

lute 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 ma

trix (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.

LAPACK version 3.0 15 June 2000

DLANGT(3)