# dlansp (l) - Linux Manuals

## NAME

DLANSP - 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, supplied in packed form

## SYNOPSIS

DOUBLE PRECISION
FUNCTION DLANSP( NORM, UPLO, N, AP, WORK )

CHARACTER NORM, UPLO

INTEGER N

DOUBLE PRECISION AP( * ), WORK( * )

## PURPOSE

DLANSP 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, supplied in packed form.

## DESCRIPTION

DLANSP returns the value

DLANSP max(abs(A(i,j))), NORM aqMaq or aqmaq

(

norm1(A),         NORM aq1aq, aqOaq or aqoaq

(

normI(A),         NORM aqIaq or aqiaq

(

normF(A),         NORM aqFaq, aqfaq, aqEaq or aqeaq 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 DLANSP as described above.
UPLO (input) CHARACTER*1
Specifies whether the upper or lower triangular part of the symmetric matrix A is supplied. = aqUaq: Upper triangular part of A is supplied
= aqLaq: Lower triangular part of A is supplied
N (input) INTEGER
The order of the matrix A. N >= 0. When N = 0, DLANSP is set to zero.
AP (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
The upper or lower triangle of the symmetric matrix A, packed columnwise in a linear array. The j-th column of A is stored in the array AP as follows: if UPLO = aqUaq, AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; if UPLO = aqLaq, AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
WORK (workspace) DOUBLE PRECISION array, dimension (MAX(1,LWORK)),
where LWORK >= N when NORM = aqIaq or aq1aq or aqOaq; otherwise, WORK is not referenced.