SRC/dstevd.f(3)

🌈 SRC/dstevd.f(3) — LAPACK Library Functions Manual 🌈

💖 NAME 💖

okay bestie, this is the page for SRC/dstevd.f — the dstevd subroutine. It's the "compute all eigenvalues and maybe eigenvectors of a real symmetric tridiagonal matrix" girlie. That's the name vibe, periodt. ✨

🦋 SYNOPSIS 🦋

🧚 Functions/Subroutines 🧚

subroutine dstevd (jobz, n, d, e, z, ldz, work, lwork, iwork, liwork,
           info)

DSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices. Yes, "OTHER matrices" is literally the phrase — iykyk. 💅

✨ Function/Subroutine Documentation ✨

Here's the full signature, character-for-character, because we do not mess with the code 🫶

subroutine dstevd (character jobz, integer n, double precision, dimension( *
     ) d, double precision, dimension( * ) e, double precision, dimension(
     ldz, * ) z, integer ldz, double precision, dimension( * ) work, integer
     lwork, integer, dimension( * ) iwork, integer liwork, integer info)

DSTEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for OTHER matrices. It's giving "all eigenvalues + optional eigenvectors" energy. 👑

🌸 Purpose 🌸

DSTEVD computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix. If eigenvectors are desired, it uses a divide and conquer algorithm. That's the whole purpose, bestie — no hidden side quests. 🫶

🎀 Parameters 🎀

• JOBZ — CHARACTER*1. It tells DSTEVD what you want: 'N' = compute eigenvalues only; 'V' = compute eigenvalues and eigenvectors. Choose your fighter. 💅
• N — INTEGER. The order of the matrix. Constraint: N >= 0.
• D — DOUBLE PRECISION array, dimension (N). On entry, it's the n diagonal elements of the tridiagonal matrix A. On exit, if INFO = 0, it holds the eigenvalues in ascending order. Slay. ✨
• E — 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. Yeah, she's gone. 😭
• Z — 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. Not even looked at. 🙈
• LDZ — INTEGER. The leading dimension of the array Z. LDZ >= 1, and if JOBZ = 'V', LDZ >= max(1,N).
• WORK — DOUBLE PRECISION array, dimension (LWORK). On exit, if INFO = 0, WORK(1) returns the optimal LWORK. It's the workspace bestie. ✨
• LWORK — INTEGER. The dimension of the array WORK. If JOBZ = 'N' or N <= 1 then LWORK must be at least 1. If JOBZ = 'V' and N > 1 then LWORK must be at least ( 1 + 4*N + N**2 ). If LWORK = -1, then a workspace query is assumed; the routine only calculates the optimal sizes of the WORK and IWORK arrays, returns these values as the first entries of the WORK and IWORK arrays, and no error message related to LWORK or LIWORK is issued by XERBLA. Query mode: iconic, honestly. 🔥
• IWORK — INTEGER array, dimension (MAX(1,LIWORK)). On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.
• LIWORK — INTEGER. The dimension of the array IWORK. If JOBZ = 'N' or N <= 1 then LIWORK must be at least 1. If JOBZ = 'V' and N > 1 then LIWORK must be at least 3+5*N. If LIWORK = -1, then a workspace query is assumed; the routine only calculates the optimal sizes of the WORK and IWORK arrays, returns these values as the first entries of the WORK and IWORK arrays, and no error message related to LWORK or LIWORK is issued by XERBLA. Same query energy, different integer array. 🧚
• INFO — INTEGER. Exit-status tea: = 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. So if you see a positive INFO, that's the algorithm saying "bestie, I couldn't make those off-diagonals zero." 💀

👑 Author 👑

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

Definition at line 155 of file dstevd.f.

🌟 Author 🌟

Generated automatically by Doxygen for LAPACK from the source code. Doxygen did the auto-generation, not me. 🫶

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SRC/dstevd.f(3) · LAPACK Version 3.12.0 — that's the source/version from the footer. The original footer doesn't show a separate date, so no date to report, bestie. Bye-bye! 💜🦋