man dstev (Fonctions bibliothèques) - compute all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A

NAME

DSTEV - compute all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A

DSTEV computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A.

JOBZ (input) CHARACTER*1: = 'N': Compute eigenvalues only;

= 'V': Compute eigenvalues and eigenvectors.
N (input) INTEGER: The order of the matrix. N >= 0.
D (input/output) DOUBLE PRECISION array, dimension (N): On entry, the n diagonal elements of the tridiagonal matrix A. On exit, if INFO = 0, the eigenvalues in ascending order.
E (input/output) DOUBLE PRECISION array, dimension (N): On entry, the (n-1) subdiagonal elements of the tridiagonal matrix A, stored in elements 1 to N-1 of E; E(N) need not be set, but is used by the routine. On exit, the contents of E are destroyed.
Z (output) DOUBLE PRECISION array, dimension (LDZ, N): If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal eigenvectors of the matrix A, with the i-th column of Z holding the eigenvector associated with D(i). If JOBZ = 'N', then Z is not referenced.
LDZ (input) INTEGER: The leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= max(1,N).
WORK (workspace) DOUBLE PRECISION array, dimension (max(1,2*N-2)): If JOBZ = 'N', WORK is not referenced.
INFO (output) INTEGER: = 0: successful exit

< 0: if INFO = -i, the i-th argument had an illegal value

> 0: if INFO = i, the algorithm failed to converge; i off-diagonal elements of E did not converge to zero.