dlantb (l) - Linux Manuals

dlantb: 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 triangular band matrix A, with ( k + 1 ) diagonals

NAME

DLANTB - 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 triangular band matrix A, with ( k + 1 ) diagonals

SYNOPSIS

DOUBLE PRECISION

FUNCTION DLANTB( NORM, UPLO, DIAG, N, K, AB, LDAB, WORK )

    

CHARACTER DIAG, NORM, UPLO

    

INTEGER K, LDAB, N

    

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

PURPOSE

DLANTB 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 triangular band matrix A, with ( k + 1 ) diagonals.

DESCRIPTION

DLANTB returns the value

DLANTB = ( 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 DLANTB as described above.

UPLO (input) CHARACTER*1

Specifies whether the matrix A is upper or lower triangular. = aqUaq: Upper triangular
= aqLaq: Lower triangular

DIAG (input) CHARACTER*1

Specifies whether or not the matrix A is unit triangular. = aqNaq: Non-unit triangular
= aqUaq: Unit triangular

N (input) INTEGER

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

K (input) INTEGER

The number of super-diagonals of the matrix A if UPLO = aqUaq, or the number of sub-diagonals of the matrix A if UPLO = aqLaq. K >= 0.

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

The upper or lower triangular 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 = aqUaq, AB(k+1+i-j,j) = A(i,j) for max(1,j-k)<=i<=j; if UPLO = aqLaq, AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+k). Note that when DIAG = aqUaq, the elements of the array AB corresponding to the diagonal elements of the matrix A are not referenced, but are assumed to be one.

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 = aqIaq; otherwise, WORK is not referenced.