slaed1 - compute the updated eigensystem of a diagonal matrix after modification by a rank-one symmetric matrix. Used by sstedc, when the original matrix is tridiagonal
SUBROUTINE SLAED1(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) INTEGER CUTPNT, INFO, LDQ, N REAL RHO INTEGER INDXQ(*), IWORK(*) REAL D(*), Q(LDQ,*), WORK(*) SUBROUTINE SLAED1_64(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) INTEGER*8 CUTPNT, INFO, LDQ, N REAL RHO INTEGER*8 INDXQ(*), IWORK(*) REAL D(*), Q(LDQ,*), WORK(*) F95 INTERFACE SUBROUTINE LAED1(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) REAL, DIMENSION(:,:) :: Q INTEGER :: N, LDQ, CUTPNT, INFO INTEGER, DIMENSION(:) :: INDXQ, IWORK REAL, DIMENSION(:) :: D, WORK REAL :: RHO SUBROUTINE LAED1_64(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) REAL, DIMENSION(:,:) :: Q INTEGER(8) :: N, LDQ, CUTPNT, INFO INTEGER(8), DIMENSION(:) :: INDXQ, IWORK REAL, DIMENSION(:) :: D, WORK REAL :: RHO C INTERFACE #include <sunperf.h> void slaed1 (int n, float *d, float *q, int ldq, int *indxq, float rho, int cutpnt, int *info); void slaed1_64 (long n, float *d, float *q, long ldq, long *indxq, float rho, long cutpnt, long *info);
Oracle Solaris Studio Performance Library slaed1(3P) NAME slaed1 - compute the updated eigensystem of a diagonal matrix after modification by a rank-one symmetric matrix. Used by sstedc, when the original matrix is tridiagonal SYNOPSIS SUBROUTINE SLAED1(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) INTEGER CUTPNT, INFO, LDQ, N REAL RHO INTEGER INDXQ(*), IWORK(*) REAL D(*), Q(LDQ,*), WORK(*) SUBROUTINE SLAED1_64(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) INTEGER*8 CUTPNT, INFO, LDQ, N REAL RHO INTEGER*8 INDXQ(*), IWORK(*) REAL D(*), Q(LDQ,*), WORK(*) F95 INTERFACE SUBROUTINE LAED1(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) REAL, DIMENSION(:,:) :: Q INTEGER :: N, LDQ, CUTPNT, INFO INTEGER, DIMENSION(:) :: INDXQ, IWORK REAL, DIMENSION(:) :: D, WORK REAL :: RHO SUBROUTINE LAED1_64(N, D, Q, LDQ, INDXQ, RHO, CUTPNT, WORK, IWORK, INFO) REAL, DIMENSION(:,:) :: Q INTEGER(8) :: N, LDQ, CUTPNT, INFO INTEGER(8), DIMENSION(:) :: INDXQ, IWORK REAL, DIMENSION(:) :: D, WORK REAL :: RHO C INTERFACE #include <sunperf.h> void slaed1 (int n, float *d, float *q, int ldq, int *indxq, float rho, int cutpnt, int *info); void slaed1_64 (long n, float *d, float *q, long ldq, long *indxq, float rho, long cutpnt, long *info); PURPOSE slaed1 computes the updated eigensystem of a diagonal matrix after mod- ification by a rank-one symmetric matrix. This routine is used only for the eigenproblem which requires all eigenvalues and eigenvectors of a tridiagonal matrix. SLAED7 handles the case in which eigenvalues only or eigenvalues and eigenvectors of a full symmetric matrix (which was reduced to tridiagonal form) are desired. T = Q(in) (D(in)+RHO*Z*Z**T) Q**T(in) = Q(out)*D(out)*Q**T(out) where Z = Q**T*u, u is a vector of length N with ones in the CUTPNT and CUTPNT + 1 th elements and zeros elsewhere. The eigenvectors of the original matrix are stored in Q, and the eigen- values are in D. The algorithm consists of three stages: The first stage consists of deflating the size of the problem when there are multiple eigenvalues or if there is a zero in the Z vector. For each such occurence the dimension of the secular equation problem is reduced by one. This stage is performed by the routine SLAED2. The second stage consists of calculating the updated eigenvalues. This is done by finding the roots of the secular equation via the routine SLAED4 (as called by SLAED3). This routine also calculates the eigen- vectors of the current problem. The final stage consists of computing the updated eigenvectors directly using the updated eigenvalues. The eigenvectors for the current problem are multiplied with the eigenvectors from the overall problem. ARGUMENTS N (input) N is INTEGER The dimension of the symmetric tridiagonal matrix. N >= 0. D (input/output) D is REAL array, dimension (N) On entry, the eigenvalues of the rank-1-perturbed matrix. On exit, the eigenvalues of the repaired matrix. Q (input/output) Q is REAL array, dimension (LDQ,N) On entry, the eigenvectors of the rank-1-perturbed matrix. On exit, the eigenvectors of the repaired tridiagonal matrix. LDQ (input) LDQ is INTEGER The leading dimension of the array Q. LDQ >= max(1,N). INDXQ (input/output) INDXQ is INTEGER array, dimension (N) On entry, the permutation which separately sorts the two sub- problems in D into ascending order. On exit, the permutation which will reintegrate the subprob- lems back into sorted order, i.e. D(INDXQ(I=1,N)) will be in ascending order. RHO (input) RHO is REAL The subdiagonal entry used to create the rank-1 modification. CUTPNT (input) CUTPNT is INTEGER The location of the last eigenvalue in the leading sub- matrix. min(1,N) <= CUTPNT <= N/2. WORK (output) WORK is REAL array, dimension (4*N+N**2) IWORK (output) IWORK is INTEGER array, dimension (4*N) INFO (output) INFO is INTEGER = 0: successful exit, < 0: if INFO = -i, the i-th argument had an illegal value, > 0: if INFO = 1, an eigenvalue did not converge. 7 Nov 2015 slaed1(3P)