CSTEQR(3)

okay so bestie, welcome to the csteqr.f(3) page from the Library Functions Manual 🌈 — that header path is literally /home/abui...RC/csteqr.f(3), and this Fortran subroutine is lowkey iconic 💅

💖 NAME 💖

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/csteqr.f — yes bestie, that’s the whole file path, character for character, no cap 🫶

✨ SYNOPSIS ✨

🌸 Functions/Subroutines 🌸

subroutine CSTEQR (compz, n, d, e, z, ldz, work, info)
    CSTEQR

one subroutine, CSTEQR, main character energy 👑

🦋 Function/Subroutine Documentation 🦋

subroutine CSTEQR (character compz, integer n, real, dimension( * ) d, real,
    dimension( * ) e, complex, dimension( ldz, * ) z, integer ldz, real,
    dimension( * ) work, integer info)
       CSTEQR

that’s the exact full signature, bestie — line breaks and all, don’t let them scare you 💀

🎀 Purpose 🎀

CSTEQR computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. periodt. 🔥

The eigenvectors of a full or band complex Hermitian matrix can also be found if CHETRD or CHPTRD or CHBTRD 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 REAL 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 REAL 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 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 REAL 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.

🚨 okay so if INFO > 0, that’s the “algorithm ran out of patience” moment — 30*N iterations, bestie. and 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. not the full win, but the tea is right there 🫖

👑 Author 👑

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

Definition at line 131 of file csteqr.f.

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code. no thoughts, just automation 🧚

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and that’s the sign-off, bestie 💖: source/version LAPACK, Version 3.12.0; footer path /home/abui...RC/csteqr.f(3); date: not separately listed in the original footer. bye and stay slaying those tridiagonal matrices 💅✨