SYNOPSIS

DOUBLE PRECISION

FUNCTION DLANSB( NORM, UPLO, N, K, AB, LDAB, WORK )

    

CHARACTER NORM, UPLO

    

INTEGER K, LDAB, N

    

DOUBLE PRECISION AB( LDAB, * ), WORK( * )

PURPOSE

DLANSB returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of an n by n symmetric band matrix A, with k super-diagonals.

DESCRIPTION

DLANSB returns the value

   DLANSB = ( 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 DLANSB as described above.

UPLO (input) CHARACTER*1

Specifies whether the upper or lower triangular part of the band matrix A is supplied. = 'U': Upper triangular part is supplied
= 'L': Lower triangular part is supplied

N (input) INTEGER

The order of the matrix A. N >= 0. When N = 0, DLANSB is set to zero.

K (input) INTEGER

The number of super-diagonals or sub-diagonals of the band matrix A. K >= 0.

AB (input) DOUBLE PRECISION array, dimension (LDAB,N)

The upper or lower triangle of the symmetric band matrix A, stored in the first K+1 rows of AB. The j-th column of A is stored in the j-th column of the array AB as follows: if UPLO = 'U', AB(k+1+i-j,j) = A(i,j) for max(1,j-k)<=i<=j; if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+k).

LDAB (input) INTEGER

The leading dimension of the array AB. LDAB >= K+1.

WORK (workspace) DOUBLE PRECISION array, dimension (MAX(1,LWORK)),

where LWORK >= N when NORM = 'I' or '1' or 'O'; otherwise, WORK is not referenced.