SUBROUTINE ZPTEQR( COMPZ, N, D, E, Z, LDZ, WORK, INFO) CHARACTER * 1 COMPZ DOUBLE COMPLEX Z(LDZ,*) INTEGER N, LDZ, INFO DOUBLE PRECISION D(*), E(*), WORK(*) SUBROUTINE ZPTEQR_64( COMPZ, N, D, E, Z, LDZ, WORK, INFO) CHARACTER * 1 COMPZ DOUBLE COMPLEX Z(LDZ,*) INTEGER*8 N, LDZ, INFO DOUBLE PRECISION D(*), E(*), WORK(*)
SUBROUTINE PTEQR( COMPZ, [N], D, E, Z, [LDZ], [WORK], [INFO]) CHARACTER(LEN=1) :: COMPZ COMPLEX(8), DIMENSION(:,:) :: Z INTEGER :: N, LDZ, INFO REAL(8), DIMENSION(:) :: D, E, WORK SUBROUTINE PTEQR_64( COMPZ, [N], D, E, Z, [LDZ], [WORK], [INFO]) CHARACTER(LEN=1) :: COMPZ COMPLEX(8), DIMENSION(:,:) :: Z INTEGER(8) :: N, LDZ, INFO REAL(8), DIMENSION(:) :: D, E, WORK
void zpteqr(char compz, int n, double *d, double *e, doublecomplex *z, int ldz, int *info);
void zpteqr_64(char compz, long n, double *d, double *e, doublecomplex *z, long ldz, long *info);
This routine computes the eigenvalues of the positive definite tridiagonal matrix to high relative accuracy. This means that if the eigenvalues range over many orders of magnitude in size, then the small eigenvalues and corresponding eigenvectors will be computed more accurately than, for example, with the standard QR method.
The eigenvectors of a full or band positive definite Hermitian matrix can also be found if CHETRD, CHPTRD, or CHBTRD has been used to reduce this matrix to tridiagonal form. (The reduction to tridiagonal form, however, may preclude the possibility of obtaining high relative accuracy in the small eigenvalues of the original matrix, if these eigenvalues range over many orders of magnitude.)