dlansy(3)

NAME

DLANSY - 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 symmetric matrix A

SYNOPSIS

DOUBLE PRECISION FUNCTION DLANSY( NORM, UPLO, N,  A,  LDA,
WORK )
    CHARACTER    NORM, UPLO
    INTEGER      LDA, N
    DOUBLE       PRECISION A( LDA, * ), WORK( * )

PURPOSE

DLANSY 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 symmetric matrix A.

DESCRIPTION

DLANSY returns the value

DLANSY = ( 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 DLANSY as

described above.

UPLO (input) CHARACTER*1

Specifies whether the upper or lower triangular

part of the symmetric matrix A is to be referenced. = 'U': Up

per triangular part of A is referenced
= 'L': Lower triangular part of A is referenced

N (input) INTEGER

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

DLANSY is set to zero.

A (input) DOUBLE PRECISION array, dimension (LDA,N)

The symmetric matrix A. If UPLO = 'U', the lead

ing n by n upper triangular part of A contains the upper triangu

lar part of the matrix A, and the strictly lower triangular part

of A is not referenced. If UPLO = 'L', the leading n by n lower

triangular part of A contains the lower triangular part of the

matrix A, and the strictly upper triangular part of A is not ref

erenced.

LDA (input) INTEGER

The leading dimension of the array A. LDA >=

max(N,1).

WORK (workspace) DOUBLE PRECISION array, dimension

(LWORK),

where LWORK >= N when NORM = 'I' or '1' or 'O';

otherwise, WORK is not referenced.

LAPACK version 3.0 15 June 2000

DLANSY(3)