# dlangt.f man page

dlangt.f

## Synopsis

### 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:

NORM

```          NORM is CHARACTER*1
Specifies the value to be returned in DLANGT as described
above.```

N

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

DL

```          DL is DOUBLE PRECISION array, dimension (N-1)
The (n-1) sub-diagonal elements of A.```

D

```          D is DOUBLE PRECISION array, dimension (N)
The diagonal elements of A.```

DU

```          DU is DOUBLE PRECISION array, dimension (N-1)
The (n-1) super-diagonal elements of A.```
Author:

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:

December 2016

Definition at line 108 of file dlangt.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page dlangt(3) is an alias of dlangt.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK