# dlangt (3) - Linux Man Pages

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 (characterNORM, integerN, 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

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 107 of file dlangt.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.