/home/abui...RC/dstev.f(3)

💅 DSTEV — like, the tridiagonal eigenvalue situation ✨

okay so bestie, this is the dstvev... no wait, dstev.f page from the LAPACK library — a Fortran library functions manual situation. It lives at /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dstev.f and honestly? iconic address. 🎀

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✨ NAME ✨

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

that's it, that's the name, she's literally just a whole file path and we respect it 👑

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🌸 SYNOPSIS 🌸

Functions/Subroutines

subroutine DSTEV (jobz, n, d, e, z, ldz, work, info)

DSTEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

like... yes queen, that's the whole assignment 💅

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🦋 Function/Subroutine Documentation 🦋

subroutine DSTEV (character jobz, integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, double precision, dimension( ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer info)

DSTEV computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices

🎀 Purpose:

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

so basically you hand her a real symmetric tridiagonal matrix A and she gives you all the eigenvalues, and if you ask nicely she'll throw in the eigenvectors too. main character energy fr fr ✨

💖 Parameters

• JOBZ — ngl this is the personality switch, she's CHARACTER*1:
  • = 'N': compute eigenvalues only — minimal effort, we love a low-effort queen;
  • = 'V': compute eigenvalues and eigenvectors — she's doing the most and honestly? slay.
• N — N is INTEGER, the order of the matrix. N >= 0. (yes bestie, zero is allowed, empty matrix rights 🫶)
• D — D is 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. organised. sorted. a whole vibe check 💅
• E — E is DOUBLE PRECISION array, dimension (N-1).
  • On entry: the (n-1) subdiagonal elements of the tridiagonal matrix A, stored in elements 1 to N-1 of E.
  • On exit: the contents of E are destroyed 😭 like not "modified", destroyed, she's gone, say your goodbyes.
• Z — Z is 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. she's not invited to this one 🙈
• LDZ — LDZ is INTEGER, the leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= max(1,N). do not fumble this one, it's giving "read the instructions" 📋
• WORK — WORK is DOUBLE PRECISION array, dimension (max(1,2*N-2)). If JOBZ = 'N', WORK is not referenced. she's just chilling in the wings 🧚
• INFO — INFO is INTEGER, and she's the gorliest gossip reporter:
  • = 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. 😭 it's giving "she tried her best"

ngl bestie, watch that INFO > 0 case — convergence failure is real and she will tell you exactly how many off-diagonal elements of E ghosted the zero. no cap.

👑 Author

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

the full friend group showed up, we love a collaborative effort 🌈

Definition at line 115 of file dstev.f. ✨

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💜 Author

Generated automatically by Doxygen for LAPACK from the source code. (yes, a robot wrote the page, no, she's not sorry 🤖💅)

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okay that's the whole thing!! all facts intact, zero details dropped, and honestly? tridiagonal matrices are lowkey underrated. bye bestie, go get those eigenvalues 🍓🦋

— LAPACK, Version 3.12.0, and the page footer date situation, signing off 🎀✨