 LAPACK  3.4.2 LAPACK: Linear Algebra PACKage
dlangt.f File Reference

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## Functions/Subroutines

DOUBLE PRECISION function dlangt (NORM, N, DL, D, DU)
DLANGT returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

## Function/Subroutine Documentation

 DOUBLE PRECISION function dlangt ( character NORM, integer N, double precision, dimension( * ) DL, double precision, dimension( * ) D, double precision, dimension( * ) DU )

DLANGT returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

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.```
Returns:
DLANGT
```    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.```
Parameters:
 [in] NORM ``` NORM is CHARACTER*1 Specifies the value to be returned in DLANGT as described above.``` [in] N ``` N is INTEGER The order of the matrix A. N >= 0. When N = 0, DLANGT is set to zero.``` [in] DL ``` DL is DOUBLE PRECISION array, dimension (N-1) The (n-1) sub-diagonal elements of A.``` [in] D ``` D is DOUBLE PRECISION array, dimension (N) The diagonal elements of A.``` [in] DU ``` DU is DOUBLE PRECISION array, dimension (N-1) The (n-1) super-diagonal elements of A.```
Date:
September 2012

Definition at line 107 of file dlangt.f.

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