DSTEIN (3) Linux Manual Page

dstein.f –

Synopsis

Functions/Subroutines

subroutine dstein (N, D, E, M, W, IBLOCK, ISPLIT, Z, LDZ, WORK, IWORK, IFAIL, INFO)
DSTEIN

Function/Subroutine Documentation

subroutine dstein (integerN, double precision, dimension( * )D, double precision, dimension( * )E, integerM, double precision, dimension( * )W, integer, dimension( * )IBLOCK, integer, dimension( * )ISPLIT, double precision, dimension( ldz, * )Z, integerLDZ, double precision, dimension( * )WORK, integer, dimension( * )IWORK, integer, dimension( * )IFAIL, integerINFO)

DSTEIN

Purpose:

 DSTEIN computes the eigenvectors of a real symmetric tridiagonal

 matrix T corresponding to specified eigenvalues, using inverse

 iteration.

 The maximum number of iterations allowed for each eigenvector is

 specified by an internal parameter MAXITS (currently set to 5).

 

Parameters:

N

 N is INTEGER

 The order of the matrix. N >= 0.

D

 D is DOUBLE PRECISION array, dimension (N)

 The n diagonal elements of the tridiagonal matrix T.

E

 E is DOUBLE PRECISION array, dimension (N-1)

 The (n-1) subdiagonal elements of the tridiagonal matrix

 T, in elements 1 to N-1.

M

 M is INTEGER

 The number of eigenvectors to be found. 0 <= M <= N.

W

 W is DOUBLE PRECISION array, dimension (N)

 The first M elements of W contain the eigenvalues for

 which eigenvectors are to be computed. The eigenvalues

 should be grouped by split-off block and ordered from

 smallest to largest within the block. ( The output array

 W from DSTEBZ with ORDER = ‘B’ is expected here. )

IBLOCK

 IBLOCK is INTEGER array, dimension (N)

 The submatrix indices associated with the corresponding

 eigenvalues in W; IBLOCK(i)=1 if eigenvalue W(i) belongs to

 the first submatrix from the top, =2 if W(i) belongs to

 the second submatrix, etc. ( The output array IBLOCK

 from DSTEBZ is expected here. )

ISPLIT

 ISPLIT is INTEGER array, dimension (N)

 The splitting points, at which T breaks up into submatrices.

 The first submatrix consists of rows/columns 1 to

 ISPLIT( 1 ), the second of rows/columns ISPLIT( 1 )+1

 through ISPLIT( 2 ), etc.

 ( The output array ISPLIT from DSTEBZ is expected here. )

Z

 Z is DOUBLE PRECISION array, dimension (LDZ, M)

 The computed eigenvectors. The eigenvector associated

 with the eigenvalue W(i) is stored in the i-th column of

 Z. Any vector which fails to converge is set to its current

 iterate after MAXITS iterations.

LDZ

 LDZ is INTEGER

 The leading dimension of the array Z. LDZ >= max(1,N).

WORK

 WORK is DOUBLE PRECISION array, dimension (5*N)

IWORK

 IWORK is INTEGER array, dimension (N)

IFAIL

 IFAIL is INTEGER array, dimension (M)

 On normal exit, all elements of IFAIL are zero.

 If one or more eigenvectors fail to converge after

 MAXITS iterations, then their indices are stored in

 array IFAIL.

INFO

 INFO is INTEGER

 = 0: successful exit.

 < 0: if INFO = -i, the i-th argument had an illegal value

 > 0: if INFO = i, then i eigenvectors failed to converge

 in MAXITS iterations. Their indices are stored in

 array IFAIL.

 

Internal Parameters:

 MAXITS INTEGER, default = 5

 The maximum number of iterations performed.

 EXTRA INTEGER, default = 2

 The number of iterations performed after norm growth

 criterion is satisfied, should be at least 1.

 

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

November 2011

Definition at line 174 of file dstein.f.

Author

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