DLANGT(3F)DLANGT(3F)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.
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DLANGT(3F)DLANGT(3F)
DU (input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) super-diagonal elements of A.
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