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# LAPACK-3

## man page of LAPACK-3

### LAPACK-3: returns the value of the one norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute

```NAME
LAPACK-3 - returns the value of the one norm, or the Frobenius norm, or
the infinity norm, or the  element  of  largest  absolute  value  of  a
complex tridiagonal matrix A

SYNOPSIS
DOUBLE PRECISION FUNCTION ZLANGT( NORM, N, DL, D, DU )

CHARACTER    NORM

INTEGER      N

COMPLEX*16   D( * ), DL( * ), DU( * )

PURPOSE
ZLANGT   returns  the value of the one norm,  or the Frobenius norm, or
the  infinity norm,  or the  element of  largest absolute value   of  a
complex tridiagonal matrix A.

DESCRIPTION
ZLANGT returns the value
ZLANGT = ( 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 ZLANGT as described
above.

N       (input) INTEGER
The order of the matrix A.  N >= 0.  When N = 0, ZLANGT is
set to zero.

DL      (input) COMPLEX*16 array, dimension (N-1)
The (n-1) sub-diagonal elements of A.

D       (input) COMPLEX*16 array, dimension (N)
The diagonal elements of A.

DU      (input) COMPLEX*16 array, dimension (N-1)
The (n-1) super-diagonal elements of A.

LAPACK auxiliary routine (versionMarch 2011                       LAPACK-3(3)
```

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