SLANST  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 symmetric tridiagonal matrix A.

    SLANST = ( 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.

          NORM is CHARACTER*1
          Specifies the value to be returned in SLANST as described
          above.

          N is INTEGER
          The order of the matrix A.  N >= 0.  When N = 0, SLANST is
          set to zero.

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

          E is REAL array, dimension (N-1)
          The (n-1) sub-diagonal or super-diagonal elements of A.