.TH "dlasd4.f" 3 "Wed Oct 15 2014" "Version 3.4.2" "LAPACK" \" -*- nroff -*-
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.SH NAME
dlasd4.f \- 
.SH SYNOPSIS
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.SS "Functions/Subroutines"

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.RI "subroutine \fBdlasd4\fP (N, I, D, Z, DELTA, RHO, SIGMA, WORK, INFO)"
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.RI "\fI\fBDLASD4\fP computes the square root of the i-th updated eigenvalue of a positive symmetric rank-one modification to a positive diagonal matrix\&. Used by dbdsdc\&. \fP"
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.SH "Function/Subroutine Documentation"
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.SS "subroutine dlasd4 (integerN, integerI, double precision, dimension( * )D, double precision, dimension( * )Z, double precision, dimension( * )DELTA, double precisionRHO, double precisionSIGMA, double precision, dimension( * )WORK, integerINFO)"

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\fBDLASD4\fP computes the square root of the i-th updated eigenvalue of a positive symmetric rank-one modification to a positive diagonal matrix\&. Used by dbdsdc\&.  
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\fBPurpose: \fP
.RS 4

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.nf
 This subroutine computes the square root of the I-th updated
 eigenvalue of a positive symmetric rank-one modification to
 a positive diagonal matrix whose entries are given as the squares
 of the corresponding entries in the array d, and that

        0 <= D(i) < D(j)  for  i < j

 and that RHO > 0. This is arranged by the calling routine, and is
 no loss in generality.  The rank-one modified system is thus

        diag( D ) * diag( D ) +  RHO * Z * Z_transpose.

 where we assume the Euclidean norm of Z is 1.

 The method consists of approximating the rational functions in the
 secular equation by simpler interpolating rational functions.
.fi
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.RE
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\fBParameters:\fP
.RS 4
\fIN\fP 
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          N is INTEGER
         The length of all arrays.
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\fII\fP 
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          I is INTEGER
         The index of the eigenvalue to be computed.  1 <= I <= N.
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\fID\fP 
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          D is DOUBLE PRECISION array, dimension ( N )
         The original eigenvalues.  It is assumed that they are in
         order, 0 <= D(I) < D(J)  for I < J.
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\fIZ\fP 
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          Z is DOUBLE PRECISION array, dimension ( N )
         The components of the updating vector.
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\fIDELTA\fP 
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          DELTA is DOUBLE PRECISION array, dimension ( N )
         If N .ne. 1, DELTA contains (D(j) - sigma_I) in its  j-th
         component.  If N = 1, then DELTA(1) = 1.  The vector DELTA
         contains the information necessary to construct the
         (singular) eigenvectors.
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\fIRHO\fP 
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          RHO is DOUBLE PRECISION
         The scalar in the symmetric updating formula.
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\fISIGMA\fP 
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          SIGMA is DOUBLE PRECISION
         The computed sigma_I, the I-th updated eigenvalue.
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\fIWORK\fP 
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          WORK is DOUBLE PRECISION array, dimension ( N )
         If N .ne. 1, WORK contains (D(j) + sigma_I) in its  j-th
         component.  If N = 1, then WORK( 1 ) = 1.
.fi
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\fIINFO\fP 
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          INFO is INTEGER
         = 0:  successful exit
         > 0:  if INFO = 1, the updating process failed.
.fi
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.RE
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\fBInternal Parameters: \fP
.RS 4

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.nf
  Logical variable ORGATI (origin-at-i?) is used for distinguishing
  whether D(i) or D(i+1) is treated as the origin.

            ORGATI = .true.    origin at i
            ORGATI = .false.   origin at i+1

  Logical variable SWTCH3 (switch-for-3-poles?) is for noting
  if we are working with THREE poles!

  MAXIT is the maximum number of iterations allowed for each
  eigenvalue.
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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\&. 
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\fBDate:\fP
.RS 4
November 2013 
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\fBContributors: \fP
.RS 4
Ren-Cang Li, Computer Science Division, University of California at Berkeley, USA 
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Definition at line 154 of file dlasd4\&.f\&.
.SH "Author"
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Generated automatically by Doxygen for LAPACK from the source code\&.