SLANGT (3lapack)

return 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

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.