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slangt

 NAME
      SLANGT - 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
      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  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 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.

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