SLANGT  -  return the value of the one norm, or the Frobe­
       nius norm, or the infinity norm, or the element of largest
       absolute value of a real tridiagonal matrix A


SYNOPSIS

       REAL FUNCTION SLANGT( NORM, N, DL, D, DU )

           CHARACTER NORM

           INTEGER   N

           REAL      D( * ), DL( * ), DU( * )


PURPOSE

       SLANGT 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

       SLANGT returns the value

          SLANGT = ( 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   Frobe­
       nius  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  SLANGT  as
               described above.

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

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

       D       (input) REAL array, dimension (N)
               The diagonal elements of A.

               The (n-1) super-diagonal elements of A.


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