SRC/dlangt.f(3)

NAME
SRC/dlangt.f

SYNOPSIS

  Functions/Subroutines
double precision function dlangt (norm, n, dl, d, du)
DLANGT returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

Function/Subroutine Documentation

  double precision function dlangt (character norm, integer n, double precision, dimension( * ) dl, double precision, dimension( * ) d, double precision, dimension( * ) du)

DLANGT returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

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.

Returns
    DLANGT

        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 consistent matrix norm.

Parameters
    NORM

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

    N

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

    DL

              DL is DOUBLE PRECISION array, dimension (N-1)
              The (n-1) sub-diagonal elements of A.

    D

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

    DU

              DU is DOUBLE PRECISION array, dimension (N-1)
              The (n-1) super-diagonal elements of A.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 105 of file dlangt.f.

Author

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