.TH "SRC/zstein.f" 3 "Version 3.12.0" "LAPACK" \" -*- nroff -*-
.ad l
.nh
.SH NAME
SRC/zstein.f
.SH SYNOPSIS
.br
.PP
.SS "Functions/Subroutines"

.in +1c
.ti -1c
.RI "subroutine \fBzstein\fP (n, d, e, m, w, iblock, isplit, z, ldz, work, iwork, ifail, info)"
.br
.RI "\fBZSTEIN\fP "
.in -1c
.SH "Function/Subroutine Documentation"
.PP 
.SS "subroutine zstein (integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, integer m, double precision, dimension( * ) w, integer, dimension( * ) iblock, integer, dimension( * ) isplit, complex*16, dimension( ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer, dimension( * ) iwork, integer, dimension( * ) ifail, integer info)"

.PP
\fBZSTEIN\fP  
.PP
\fBPurpose:\fP
.RS 4

.PP
.nf
 ZSTEIN 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)\&.

 Although the eigenvectors are real, they are stored in a complex
 array, which may be passed to ZUNMTR or ZUPMTR for back
 transformation to the eigenvectors of a complex Hermitian matrix
 which was reduced to tridiagonal form\&.
.fi
.PP
 
.RE
.PP
\fBParameters\fP
.RS 4
\fIN\fP 
.PP
.nf
          N is INTEGER
          The order of the matrix\&.  N >= 0\&.
.fi
.PP
.br
\fID\fP 
.PP
.nf
          D is DOUBLE PRECISION array, dimension (N)
          The n diagonal elements of the tridiagonal matrix T\&.
.fi
.PP
.br
\fIE\fP 
.PP
.nf
          E is DOUBLE PRECISION array, dimension (N-1)
          The (n-1) subdiagonal elements of the tridiagonal matrix
          T, stored in elements 1 to N-1\&.
.fi
.PP
.br
\fIM\fP 
.PP
.nf
          M is INTEGER
          The number of eigenvectors to be found\&.  0 <= M <= N\&.
.fi
.PP
.br
\fIW\fP 
.PP
.nf
          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\&. )
.fi
.PP
.br
\fIIBLOCK\fP 
.PP
.nf
          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\&. )
.fi
.PP
.br
\fIISPLIT\fP 
.PP
.nf
          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\&. )
.fi
.PP
.br
\fIZ\fP 
.PP
.nf
          Z is COMPLEX*16 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\&.
          The imaginary parts of the eigenvectors are set to zero\&.
.fi
.PP
.br
\fILDZ\fP 
.PP
.nf
          LDZ is INTEGER
          The leading dimension of the array Z\&.  LDZ >= max(1,N)\&.
.fi
.PP
.br
\fIWORK\fP 
.PP
.nf
          WORK is DOUBLE PRECISION array, dimension (5*N)
.fi
.PP
.br
\fIIWORK\fP 
.PP
.nf
          IWORK is INTEGER array, dimension (N)
.fi
.PP
.br
\fIIFAIL\fP 
.PP
.nf
          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\&.
.fi
.PP
.br
\fIINFO\fP 
.PP
.nf
          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\&.
.fi
.PP
 
.RE
.PP
\fBInternal Parameters:\fP
.RS 4

.PP
.nf
  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\&.
.fi
.PP
 
.RE
.PP
\fBAuthor\fP
.RS 4
Univ\&. of Tennessee 
.PP
Univ\&. of California Berkeley 
.PP
Univ\&. of Colorado Denver 
.PP
NAG Ltd\&. 
.RE
.PP

.PP
Definition at line \fB180\fP of file \fBzstein\&.f\fP\&.
.SH "Author"
.PP 
Generated automatically by Doxygen for LAPACK from the source code\&.