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

.in +1c
.ti -1c
.RI "subroutine \fBdlarrk\fP (n, iw, gl, gu, d, e2, pivmin, reltol, w, werr, info)"
.br
.RI "\fBDLARRK\fP computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy\&. "
.in -1c
.SH "Function/Subroutine Documentation"
.PP 
.SS "subroutine dlarrk (integer n, integer iw, double precision gl, double precision gu, double precision, dimension( * ) d, double precision, dimension( * ) e2, double precision pivmin, double precision reltol, double precision w, double precision werr, integer info)"

.PP
\fBDLARRK\fP computes one eigenvalue of a symmetric tridiagonal matrix T to suitable accuracy\&.  
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\fBPurpose:\fP
.RS 4

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.nf
!>
!> DLARRK computes one eigenvalue of a symmetric tridiagonal
!> matrix T to suitable accuracy\&. This is an auxiliary code to be
!> called from DSTEMR\&.
!>
!> To avoid overflow, the matrix must be scaled so that its
!> largest element is no greater than overflow**(1/2) * underflow**(1/4) in absolute value, and for greatest
!> accuracy, it should not be much smaller than that\&.
!>
!> See W\&. Kahan , Report CS41, Computer Science Dept\&., Stanford
!> University, July 21, 1966\&.
!> 
.fi
.PP
 
.RE
.PP
\fBParameters\fP
.RS 4
\fIN\fP 
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!>          N is INTEGER
!>          The order of the tridiagonal matrix T\&.  N >= 0\&.
!> 
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.br
\fIIW\fP 
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!>          IW is INTEGER
!>          The index of the eigenvalues to be returned\&.
!> 
.fi
.PP
.br
\fIGL\fP 
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!>          GL is DOUBLE PRECISION
!> 
.fi
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\fIGU\fP 
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!>          GU is DOUBLE PRECISION
!>          An upper and a lower bound on the eigenvalue\&.
!> 
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.PP
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\fID\fP 
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!>          D is DOUBLE PRECISION array, dimension (N)
!>          The n diagonal elements of the tridiagonal matrix T\&.
!> 
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.br
\fIE2\fP 
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!>          E2 is DOUBLE PRECISION array, dimension (N-1)
!>          The (n-1) squared off-diagonal elements of the tridiagonal matrix T\&.
!> 
.fi
.PP
.br
\fIPIVMIN\fP 
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!>          PIVMIN is DOUBLE PRECISION
!>          The minimum pivot allowed in the Sturm sequence for T\&.
!> 
.fi
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.br
\fIRELTOL\fP 
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.nf
!>          RELTOL is DOUBLE PRECISION
!>          The minimum relative width of an interval\&.  When an interval
!>          is narrower than RELTOL times the larger (in
!>          magnitude) endpoint, then it is considered to be
!>          sufficiently small, i\&.e\&., converged\&.  Note: this should
!>          always be at least radix*machine epsilon\&.
!> 
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.br
\fIW\fP 
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!>          W is DOUBLE PRECISION
!> 
.fi
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.br
\fIWERR\fP 
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!>          WERR is DOUBLE PRECISION
!>          The error bound on the corresponding eigenvalue approximation
!>          in W\&.
!> 
.fi
.PP
.br
\fIINFO\fP 
.PP
.nf
!>          INFO is INTEGER
!>          = 0:       Eigenvalue converged
!>          = -1:      Eigenvalue did NOT converge
!> 
.fi
.PP
 
.RE
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\fBInternal Parameters:\fP
.RS 4

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!>  FUDGE   DOUBLE PRECISION, default = 2
!>          A  to widen the Gershgorin intervals\&.
!> 
.fi
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.RE
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\fBAuthor\fP
.RS 4
Univ\&. of Tennessee 

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Univ\&. of California Berkeley 

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Univ\&. of Colorado Denver 

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NAG Ltd\&. 
.RE
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Definition at line \fB143\fP of file \fBdlarrk\&.f\fP\&.
.SH "Author"
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Generated automatically by Doxygen for LAPACK from the source code\&.