dlangt

Langue: en

Version: 318656 (ubuntu - 07/07/09)

Section: 3 (Bibliothèques de fonctions)

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.