ZSTEQR(3)

📦 version 3.12.0, in opensuse-leap 16.0

💖 NAME 💖

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/zsteqr.f

okay so this is the glow-up of the ZSTEQR(3) page — yes, the Library Functions Manual one — and the file it's serving is that path right above. bestie, we're about to get into eigenvalues and it's gonna be a whole vibe. 💅

✨ SYNOPSIS ✨

Functions/Subroutines
    subroutine ZSTEQR (compz, n, d, e, z, ldz, work, info)
        ZSTEQR

🦋 Function/Subroutine Documentation 🦋

subroutine ZSTEQR (character compz, integer n, double precision, dimension(
    * ) d, double precision, dimension( * ) e, complex*16, dimension( ldz, *
    ) z, integer ldz, double precision, dimension( * ) work, integer info)

ZSTEQR — the subroutine in question, no cap. 👑

🎀 Purpose 🎀

okay so ZSTEQR computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. obsessed with the range here: the eigenvectors of a full or band complex Hermitian matrix can also be found if ZHETRD or ZHPTRD or ZHBTRD has been used to reduce this matrix to tridiagonal form. ✨

🌸 Parameters 🌸

💅 COMPZ

COMPZ is CHARACTER*1

  • = 'N': Compute eigenvalues only.
  • = 'V': Compute eigenvalues and eigenvectors of the original Hermitian matrix. On entry, Z must contain the unitary 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.

🎀 N

N is INTEGER

The order of the matrix. N >= 0.

🍓 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.

🦋 E

E is DOUBLE PRECISION array, dimension (N-1)

On entry, the (n-1) subdiagonal elements of the tridiagonal matrix.

On exit, E has been destroyed.

💜 Z

Z is COMPLEX*16 array, dimension (LDZ, N)

On entry, if COMPZ = 'V', then Z contains the unitary 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 Hermitian matrix, and if COMPZ = 'I', Z contains the orthonormal eigenvectors of the symmetric tridiagonal matrix.

If COMPZ = 'N', then Z is not referenced.

🌈 LDZ

LDZ is INTEGER

The leading dimension of the array Z. LDZ >= 1, and if eigenvectors are desired, then LDZ >= max(1,N).

🌟 WORK

WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2))

If COMPZ = 'N', then WORK is not referenced.

🔥 INFO

INFO is INTEGER

  • = 0: successful exit
  • < 0: if INFO = -i, the i-th 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 unitarily similar to the original matrix.

👑 Author 👑

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 131 of file zsteqr.f.

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

mwah 💋 — signing off with LAPACK, Version 3.12.0, source /home/abui...RC/zsteqr.f(3). 🫶

📦 where this page comes from