SSYEVD(3)

🌸 ssyevd.f(3) — the SSYEVD glow-up 🌸

okay so bestie, welcome to the manual page for ssyevd.f(3), straight out of LAPACK land 💅 this is the tea on SSYEVD, and trust, it's a whole main-character subroutine. buckle up 🎀

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✨ NAME ✨

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

like, that's the literal whole path. she lives there. that's her address 🏠💖

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine SSYEVD (jobz, uplo, n, a, lda, w, work, lwork, iwork, liwork,
    info)

SSYEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices

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✨ Function/Subroutine Documentation ✨

subroutine SSYEVD (character jobz, character uplo, integer n, real,
    dimension( lda, * ) a, integer lda, real, dimension( * ) w, real,
    dimension( * ) work, integer lwork, integer, dimension( * ) iwork,
    integer liwork, integer info)

SSYEVD computes the eigenvalues and, optionally, the left and/or right eigenvectors for SY matrices

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💜 Purpose 💜

ok so picture this: SSYEVD computes all eigenvalues and, if you want them, the eigenvectors of a real symmetric matrix A. if eigenvectors are desired, it uses a divide and conquer algorithm. iconic behaviour honestly 👑

and because of large use of BLAS of level 3, SSYEVD needs N**2 more workspace than SSYEVX. that's the tradeoff bestie, she's hungry for memory but she's fast 🔥

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🦋 Parameters 🦋

JOBZ

JOBZ is CHARACTER*1

• = 'N': Compute eigenvalues only;
• = 'V': Compute eigenvalues and eigenvectors.

UPLO

UPLO is CHARACTER*1

• = 'U': Upper triangle of A is stored;
• = 'L': Lower triangle of A is stored.

N

N is INTEGER

The order of the matrix A. N >= 0.

A

A is REAL array, dimension (LDA, N)

On entry, the symmetric matrix A. If UPLO = 'U', the leading N-by-N upper triangular part of A contains the upper triangular part of the matrix A. If UPLO = 'L', the leading N-by-N lower triangular part of A contains the lower triangular part of the matrix A.

On exit, if JOBZ = 'V', then if INFO = 0, A contains the orthonormal eigenvectors of the matrix A.

If JOBZ = 'N', then on exit the lower triangle (if UPLO='L') or the upper triangle (if UPLO='U') of A, including the diagonal, is destroyed. 😭 she ate and left no crumbs, literally, that data is GONE

LDA

LDA is INTEGER

The leading dimension of the array A. LDA >= max(1,N).

W

W is REAL array, dimension (N)

If INFO = 0, the eigenvalues in ascending order. cute, sorted, organised ✨

WORK

WORK is REAL array, dimension (LWORK)

On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

LWORK

LWORK is INTEGER

The dimension of the array WORK.

• If N <= 1, LWORK must be at least 1.
• If JOBZ = 'N' and N > 1, LWORK must be at least 2*N+1.
• If JOBZ = 'V' and N > 1, LWORK must be at least 1 + 6*N + 2*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.

IWORK

IWORK is INTEGER array, dimension (MAX(1,LIWORK))

On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK.

LIWORK

LIWORK is INTEGER

The dimension of the array IWORK.

• If N <= 1, LIWORK must be at least 1.
• If JOBZ = 'N' and N > 1, LIWORK must be at least 1.
• If JOBZ = 'V' and N > 1, 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.

INFO

INFO is INTEGER

• = 0: successful exit
• < 0: if INFO = -i, the i-th argument had an illegal value
• > 0: if INFO = i and JOBZ = 'N', then the algorithm failed to converge; i off-diagonal elements of an intermediate tridiagonal form did not converge to zero; if INFO = i and JOBZ = 'V', then the algorithm failed to compute an eigenvalue while working on the submatrix lying in rows and columns INFO/(N+1) through mod(INFO,N+1).

ngl a positive INFO is the "she tried her best but she did NOT converge" vibe check 💀

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👑 Author 👑

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

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🧚 Contributors 🧚

Jeff Rutter, Computer Science Division, University of California at Berkeley, USA

Modified by Francoise Tisseur, University of Tennessee

Modified description of INFO. Sven, 16 Feb 05.

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Definition at line 174 of file ssyevd.f.

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🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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and that's the whole page bestie, no skips, no cap 🫶

LAPACK — Version 3.12.0 — /home/abui...RC/ssyevd.f(3)

mwah, go forth and diagonalise 💋🌸🦋