LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  slarrv (N, VL, VU, D, L, PIVMIN, ISPLIT, M, DOL, DOU, MINRGP, RTOL1, RTOL2, W, WERR, WGAP, IBLOCK, INDEXW, GERS, Z, LDZ, ISUPPZ, WORK, IWORK, INFO) 
SLARRV computes the eigenvectors of the tridiagonal matrix T = L D LT given L, D and the eigenvalues of L D LT. 
subroutine slarrv  (  integer  N, 
real  VL,  
real  VU,  
real, dimension( * )  D,  
real, dimension( * )  L,  
real  PIVMIN,  
integer, dimension( * )  ISPLIT,  
integer  M,  
integer  DOL,  
integer  DOU,  
real  MINRGP,  
real  RTOL1,  
real  RTOL2,  
real, dimension( * )  W,  
real, dimension( * )  WERR,  
real, dimension( * )  WGAP,  
integer, dimension( * )  IBLOCK,  
integer, dimension( * )  INDEXW,  
real, dimension( * )  GERS,  
real, dimension( ldz, * )  Z,  
integer  LDZ,  
integer, dimension( * )  ISUPPZ,  
real, dimension( * )  WORK,  
integer, dimension( * )  IWORK,  
integer  INFO  
) 
SLARRV computes the eigenvectors of the tridiagonal matrix T = L D LT given L, D and the eigenvalues of L D LT.
Download SLARRV + dependencies [TGZ] [ZIP] [TXT]SLARRV computes the eigenvectors of the tridiagonal matrix T = L D L**T given L, D and APPROXIMATIONS to the eigenvalues of L D L**T. The input eigenvalues should have been computed by SLARRE.
[in]  N  N is INTEGER The order of the matrix. N >= 0. 
[in]  VL  VL is REAL 
[in]  VU  VU is REAL Lower and upper bounds of the interval that contains the desired eigenvalues. VL < VU. Needed to compute gaps on the left or right end of the extremal eigenvalues in the desired RANGE. 
[in,out]  D  D is REAL array, dimension (N) On entry, the N diagonal elements of the diagonal matrix D. On exit, D may be overwritten. 
[in,out]  L  L is REAL array, dimension (N) On entry, the (N1) subdiagonal elements of the unit bidiagonal matrix L are in elements 1 to N1 of L (if the matrix is not splitted.) At the end of each block is stored the corresponding shift as given by SLARRE. On exit, L is overwritten. 
[in]  PIVMIN  PIVMIN is REAL The minimum pivot allowed in the Sturm sequence. 
[in]  ISPLIT  ISPLIT is INTEGER array, dimension (N) The splitting points, at which T breaks up into blocks. The first block consists of rows/columns 1 to ISPLIT( 1 ), the second of rows/columns ISPLIT( 1 )+1 through ISPLIT( 2 ), etc. 
[in]  M  M is INTEGER The total number of input eigenvalues. 0 <= M <= N. 
[in]  DOL  DOL is INTEGER 
[in]  DOU  DOU is INTEGER If the user wants to compute only selected eigenvectors from all the eigenvalues supplied, he can specify an index range DOL:DOU. Or else the setting DOL=1, DOU=M should be applied. Note that DOL and DOU refer to the order in which the eigenvalues are stored in W. If the user wants to compute only selected eigenpairs, then the columns DOL1 to DOU+1 of the eigenvector space Z contain the computed eigenvectors. All other columns of Z are set to zero. 
[in]  MINRGP  MINRGP is REAL 
[in]  RTOL1  RTOL1 is REAL 
[in]  RTOL2  RTOL2 is REAL Parameters for bisection. An interval [LEFT,RIGHT] has converged if RIGHTLEFT.LT.MAX( RTOL1*GAP, RTOL2*MAX(LEFT,RIGHT) ) 
[in,out]  W  W is REAL array, dimension (N) The first M elements of W contain the APPROXIMATE eigenvalues for which eigenvectors are to be computed. The eigenvalues should be grouped by splitoff block and ordered from smallest to largest within the block ( The output array W from SLARRE is expected here ). Furthermore, they are with respect to the shift of the corresponding root representation for their block. On exit, W holds the eigenvalues of the UNshifted matrix. 
[in,out]  WERR  WERR is REAL array, dimension (N) The first M elements contain the semiwidth of the uncertainty interval of the corresponding eigenvalue in W 
[in,out]  WGAP  WGAP is REAL array, dimension (N) The separation from the right neighbor eigenvalue in W. 
[in]  IBLOCK  IBLOCK is INTEGER array, dimension (N) The indices of the blocks (submatrices) associated with the corresponding eigenvalues in W; IBLOCK(i)=1 if eigenvalue W(i) belongs to the first block from the top, =2 if W(i) belongs to the second block, etc. 
[in]  INDEXW  INDEXW is INTEGER array, dimension (N) The indices of the eigenvalues within each block (submatrix); for example, INDEXW(i)= 10 and IBLOCK(i)=2 imply that the ith eigenvalue W(i) is the 10th eigenvalue in the second block. 
[in]  GERS  GERS is REAL array, dimension (2*N) The N Gerschgorin intervals (the ith Gerschgorin interval is (GERS(2*i1), GERS(2*i)). The Gerschgorin intervals should be computed from the original UNshifted matrix. 
[out]  Z  Z is REAL array, dimension (LDZ, max(1,M) ) If INFO = 0, the first M columns of Z contain the orthonormal eigenvectors of the matrix T corresponding to the input eigenvalues, with the ith column of Z holding the eigenvector associated with W(i). Note: the user must ensure that at least max(1,M) columns are supplied in the array Z. 
[in]  LDZ  LDZ is INTEGER The leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= max(1,N). 
[out]  ISUPPZ  ISUPPZ is INTEGER array, dimension ( 2*max(1,M) ) The support of the eigenvectors in Z, i.e., the indices indicating the nonzero elements in Z. The Ith eigenvector is nonzero only in elements ISUPPZ( 2*I1 ) through ISUPPZ( 2*I ). 
[out]  WORK  WORK is REAL array, dimension (12*N) 
[out]  IWORK  IWORK is INTEGER array, dimension (7*N) 
[out]  INFO  INFO is INTEGER = 0: successful exit > 0: A problem occured in SLARRV. < 0: One of the called subroutines signaled an internal problem. Needs inspection of the corresponding parameter IINFO for further information. =1: Problem in SLARRB when refining a child's eigenvalues. =2: Problem in SLARRF when computing the RRR of a child. When a child is inside a tight cluster, it can be difficult to find an RRR. A partial remedy from the user's point of view is to make the parameter MINRGP smaller and recompile. However, as the orthogonality of the computed vectors is proportional to 1/MINRGP, the user should be aware that he might be trading in precision when he decreases MINRGP. =3: Problem in SLARRB when refining a single eigenvalue after the Rayleigh correction was rejected. = 5: The Rayleigh Quotient Iteration failed to converge to full accuracy in MAXITR steps. 
Definition at line 280 of file slarrv.f.