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NAME
     dlangt - return the value of the one norm, or the  Frobenius
     norm,  or the infinity norm, or the element of largest abso-
     lute value of a real tridiagonal matrix A

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

     CHARACTER NORM

     INTEGER N

     DOUBLE PRECISION D( * ), DL( * ), DU( * )



     #include <sunperf.h>

     double dlangt(char norm, int n, double *dl, double *d,  dou-
               ble *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.


DESCRIPTION
     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  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.

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