dlangt.f File Reference

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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.

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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.

Download DLANGT + dependencies [TGZ] [ZIP] [TXT]

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:

[in]	NORM	NORM is CHARACTER*1 Specifies the value to be returned in DLANGT as described above.
[in]	N	N is INTEGER The order of the matrix A. N >= 0. When N = 0, DLANGT is set to zero.
[in]	DL	DL is DOUBLE PRECISION array, dimension (N-1) The (n-1) sub-diagonal elements of A.
[in]	D	D is DOUBLE PRECISION array, dimension (N) The diagonal elements of A.
[in]	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.

Date:

September 2012

Definition at line 107 of file dlangt.f.

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