LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

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Functions/Subroutines  
subroutine  dsteqr (COMPZ, N, D, E, Z, LDZ, WORK, INFO) 
DSTEQR 
subroutine dsteqr  (  character  COMPZ, 
integer  N,  
double precision, dimension( * )  D,  
double precision, dimension( * )  E,  
double precision, dimension( ldz, * )  Z,  
integer  LDZ,  
double precision, dimension( * )  WORK,  
integer  INFO  
) 
DSTEQR
Download DSTEQR + dependencies [TGZ] [ZIP] [TXT]DSTEQR computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. The eigenvectors of a full or band symmetric matrix can also be found if DSYTRD or DSPTRD or DSBTRD has been used to reduce this matrix to tridiagonal form.
[in]  COMPZ  COMPZ is CHARACTER*1 = 'N': Compute eigenvalues only. = 'V': Compute eigenvalues and eigenvectors of the original symmetric matrix. On entry, Z must contain the orthogonal matrix used to reduce the original matrix to tridiagonal form. = 'I': Compute eigenvalues and eigenvectors of the tridiagonal matrix. Z is initialized to the identity matrix. 
[in]  N  N is INTEGER The order of the matrix. N >= 0. 
[in,out]  D  D is DOUBLE PRECISION array, dimension (N) On entry, the diagonal elements of the tridiagonal matrix. On exit, if INFO = 0, the eigenvalues in ascending order. 
[in,out]  E  E is DOUBLE PRECISION array, dimension (N1) On entry, the (n1) subdiagonal elements of the tridiagonal matrix. On exit, E has been destroyed. 
[in,out]  Z  Z is DOUBLE PRECISION array, dimension (LDZ, N) On entry, if COMPZ = 'V', then Z contains the orthogonal matrix used in the reduction to tridiagonal form. On exit, if INFO = 0, then if COMPZ = 'V', Z contains the orthonormal eigenvectors of the original symmetric matrix, and if COMPZ = 'I', Z contains the orthonormal eigenvectors of the symmetric tridiagonal matrix. If COMPZ = 'N', then Z is not referenced. 
[in]  LDZ  LDZ is INTEGER The leading dimension of the array Z. LDZ >= 1, and if eigenvectors are desired, then LDZ >= max(1,N). 
[out]  WORK  WORK is DOUBLE PRECISION array, dimension (max(1,2*N2)) If COMPZ = 'N', then WORK is not referenced. 
[out]  INFO  INFO is INTEGER = 0: successful exit < 0: if INFO = i, the ith argument had an illegal value > 0: the algorithm has failed to find all the eigenvalues in a total of 30*N iterations; if INFO = i, then i elements of E have not converged to zero; on exit, D and E contain the elements of a symmetric tridiagonal matrix which is orthogonally similar to the original matrix. 
Definition at line 132 of file dsteqr.f.