SLAED3 (3)  Linux Manuals
NAME
slaed3.f 
SYNOPSIS
Functions/Subroutines
subroutine slaed3 (K, N, N1, D, Q, LDQ, RHO, DLAMDA, Q2, INDX, CTOT, W, S, INFO)
SLAED3 used by sstedc. Finds the roots of the secular equation and updates the eigenvectors. Used when the original matrix is tridiagonal.
Function/Subroutine Documentation
subroutine slaed3 (integerK, integerN, integerN1, real, dimension( * )D, real, dimension( ldq, * )Q, integerLDQ, realRHO, real, dimension( * )DLAMDA, real, dimension( * )Q2, integer, dimension( * )INDX, integer, dimension( * )CTOT, real, dimension( * )W, real, dimension( * )S, integerINFO)
SLAED3 used by sstedc. Finds the roots of the secular equation and updates the eigenvectors. Used when the original matrix is tridiagonal.
Purpose:

SLAED3 finds the roots of the secular equation, as defined by the values in D, W, and RHO, between 1 and K. It makes the appropriate calls to SLAED4 and then updates the eigenvectors by multiplying the matrix of eigenvectors of the pair of eigensystems being combined by the matrix of eigenvectors of the KbyK system which is solved here. This code makes very mild assumptions about floating point arithmetic. It will work on machines with a guard digit in add/subtract, or on those binary machines without guard digits which subtract like the Cray XMP, Cray YMP, Cray C90, or Cray2. It could conceivably fail on hexadecimal or decimal machines without guard digits, but we know of none.
Parameters:

K
K is INTEGER The number of terms in the rational function to be solved by SLAED4. K >= 0.
NN is INTEGER The number of rows and columns in the Q matrix. N >= K (deflation may result in N>K).
N1N1 is INTEGER The location of the last eigenvalue in the leading submatrix. min(1,N) <= N1 <= N/2.
DD is REAL array, dimension (N) D(I) contains the updated eigenvalues for 1 <= I <= K.
QQ is REAL array, dimension (LDQ,N) Initially the first K columns are used as workspace. On output the columns 1 to K contain the updated eigenvectors.
LDQLDQ is INTEGER The leading dimension of the array Q. LDQ >= max(1,N).
RHORHO is REAL The value of the parameter in the rank one update equation. RHO >= 0 required.
DLAMDADLAMDA is REAL array, dimension (K) The first K elements of this array contain the old roots of the deflated updating problem. These are the poles of the secular equation. May be changed on output by having lowest order bit set to zero on Cray XMP, Cray YMP, Cray2, or Cray C90, as described above.
Q2Q2 is REAL array, dimension (LDQ2, N) The first K columns of this matrix contain the nondeflated eigenvectors for the split problem.
INDXINDX is INTEGER array, dimension (N) The permutation used to arrange the columns of the deflated Q matrix into three groups (see SLAED2). The rows of the eigenvectors found by SLAED4 must be likewise permuted before the matrix multiply can take place.
CTOTCTOT is INTEGER array, dimension (4) A count of the total number of the various types of columns in Q, as described in INDX. The fourth column type is any column which has been deflated.
WW is REAL array, dimension (K) The first K elements of this array contain the components of the deflationadjusted updating vector. Destroyed on output.
SS is REAL array, dimension (N1 + 1)*K Will contain the eigenvectors of the repaired matrix which will be multiplied by the previously accumulated eigenvectors to update the system.
INFOINFO is INTEGER = 0: successful exit. < 0: if INFO = i, the ith argument had an illegal value. > 0: if INFO = 1, an eigenvalue did not converge
Author:

Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
 September 2012
Contributors:

Jeff Rutter, Computer Science Division, University of California at Berkeley, USA
Modified by Francoise Tisseur, University of Tennessee
Definition at line 185 of file slaed3.f.
Author
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