SSTEQR(3)

💅 NAME 💅

Okay bestie, this page is from the LAPACK Library Functions Manual (manual name folded in near the top, exactly as requested 💖). It is the manual entry for this exact file:

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

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✨ SYNOPSIS ✨

Functions/Subroutines

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

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🫶 Function/Subroutine Documentation 🫶

Here’s the full signature, no cap:

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

And the subroutine name is literally SSTEQR.

🌸 Purpose 🌸

SSTEQR computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method. The eigenvectors of a full or band symmetric matrix can also be found if SSYTRD or SSPTRD or SSBTRD has been used to reduce this matrix to tridiagonal form. Obsessed with the clarity 💅

🎀 Parameters 🎀

• COMPZ — COMPZ is CHARACTER*1. Here’s the vibe check:
  • 'N' — compute eigenvalues only.
  • 'V' — compute eigenvalues and eigenvectors of the original symmetric matrix. On entry, Z must contain the orthogonal 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 REAL array, dimension (LDZ, N). On entry, if COMPZ = 'V', then Z contains the orthogonal 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 symmetric 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 orthogonally similar to the original matrix.

👑 Author 👑

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

Definition at line 130 of file ssteqr.f.

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🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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Cute sign-off, bestie: the footer brings LAPACK Version 3.12.0 and the page path /home/abui...RC/ssteqr.f(3) — that’s the source/version/date-footer situation, and this manual page is officially done 💖✨