dlangt3lapack
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
Usage
- 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.
Overview
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 consistent 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. |
DU (input) DOUBLE PRECISION array, dimension (N-1)
|
The (n-1) super-diagonal elements of A. |