ddisna.f File Reference

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Functions/Subroutines
subroutine	ddisna (JOB, M, N, D, SEP, INFO)
	DDISNA

---

Function/Subroutine Documentation

subroutine ddisna	(	character	JOB,
		integer	M,
		integer	N,
		double precision, dimension( * )	D,
		double precision, dimension( * )	SEP,
		integer	INFO
	)

DDISNA

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Purpose:

 DDISNA computes the reciprocal condition numbers for the eigenvectors
 of a real symmetric or complex Hermitian matrix or for the left or
 right singular vectors of a general m-by-n matrix. The reciprocal
 condition number is the 'gap' between the corresponding eigenvalue or
 singular value and the nearest other one.

 The bound on the error, measured by angle in radians, in the I-th
 computed vector is given by

        DLAMCH( 'E' ) * ( ANORM / SEP( I ) )

 where ANORM = 2-norm(A) = max( abs( D(j) ) ).  SEP(I) is not allowed
 to be smaller than DLAMCH( 'E' )*ANORM in order to limit the size of
 the error bound.

 DDISNA may also be used to compute error bounds for eigenvectors of
 the generalized symmetric definite eigenproblem.

Parameters:

[in]	JOB	JOB is CHARACTER*1 Specifies for which problem the reciprocal condition numbers should be computed: = 'E': the eigenvectors of a symmetric/Hermitian matrix; = 'L': the left singular vectors of a general matrix; = 'R': the right singular vectors of a general matrix.
[in]	M	M is INTEGER The number of rows of the matrix. M >= 0.
[in]	N	N is INTEGER If JOB = 'L' or 'R', the number of columns of the matrix, in which case N >= 0. Ignored if JOB = 'E'.
[in]	D	D is DOUBLE PRECISION array, dimension (M) if JOB = 'E' dimension (min(M,N)) if JOB = 'L' or 'R' The eigenvalues (if JOB = 'E') or singular values (if JOB = 'L' or 'R') of the matrix, in either increasing or decreasing order. If singular values, they must be non-negative.
[out]	SEP	SEP is DOUBLE PRECISION array, dimension (M) if JOB = 'E' dimension (min(M,N)) if JOB = 'L' or 'R' The reciprocal condition numbers of the vectors.
[out]	INFO	INFO is INTEGER = 0: successful exit. < 0: if INFO = -i, the i-th argument had an illegal value.

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

November 2011

Definition at line 118 of file ddisna.f.

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