SRC/sstein.f(3)

💖 SRC/sstein.f — NAME 💖

Bestie, this is the manual page for SRC/sstein.f, straight out of the Library Functions Manual. It's giving “I do linear algebra and I do it fabulously,” no cap. ✨

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🌟 SYNOPSIS 🌟

Functions/Subroutines

• subroutine sstein (n, d, e, m, w, iblock, isplit, z, ldz, work, iwork, ifail, info) — SSTEIN, the subroutine herself.

subroutine sstein (n, d, e, m, w, iblock, isplit, z, ldz, work, iwork,
    ifail, info)

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🦋 Function/Subroutine Documentation 🦋

SSTEIN

subroutine sstein (integer n, real, dimension( * ) d, real, dimension( * )
    e, integer m, real, dimension( * ) w, integer, dimension( * ) iblock,
    integer, dimension( * ) isplit, real, dimension( ldz, * ) z, integer
    ldz, real, dimension( * ) work, integer, dimension( * ) iwork, integer,
    dimension( * ) ifail, integer info)

Purpose 💖

Okay so the whole vibe: SSTEIN computes the eigenvectors of a real symmetric tridiagonal matrix T corresponding to specified eigenvalues, using inverse iteration.

The maximum number of iterations allowed for each eigenvector is specified by an internal parameter MAXITS (currently set to 5). Periodt. 💅

Parameters 🎀

• N — INTEGER. The order of the matrix. N >= 0.
• D — REAL array, dimension (N). The n diagonal elements of the tridiagonal matrix T.
• E — REAL array, dimension (N-1). The (n-1) subdiagonal elements of the tridiagonal matrix T, in elements 1 to N-1.
• M — INTEGER. The number of eigenvectors to be found. 0 <= M <= N.
• W — REAL array, dimension (N). The first M elements of W contain the eigenvalues for which eigenvectors are to be computed. The eigenvalues should be grouped by split-off block and ordered from smallest to largest within the block. (The output array W from SSTEBZ with ORDER = 'B' is expected here.)
• IBLOCK — INTEGER array, dimension (N). The submatrix indices associated with the corresponding eigenvalues in W; IBLOCK(i)=1 if eigenvalue W(i) belongs to the first submatrix from the top, =2 if W(i) belongs to the second submatrix, etc. (The output array IBLOCK from SSTEBZ is expected here.)
• ISPLIT — INTEGER array, dimension (N). The splitting points, at which T breaks up into submatrices. The first submatrix consists of rows/columns 1 to ISPLIT( 1 ), the second of rows/columns ISPLIT( 1 )+1 through ISPLIT( 2 ), etc. (The output array ISPLIT from SSTEBZ is expected here.)
• Z — REAL array, dimension (LDZ, M). The computed eigenvectors. The eigenvector associated with the eigenvalue W(i) is stored in the i-th column of Z. Any vector which fails to converge is set to its current iterate after MAXITS iterations.
• LDZ — INTEGER. The leading dimension of the array Z. LDZ >= max(1,N).
• WORK — REAL array, dimension (5*N).
• IWORK — INTEGER array, dimension (N).
• IFAIL — INTEGER array, dimension (M). On normal exit, all elements of IFAIL are zero. If one or more eigenvectors fail to converge after MAXITS iterations, then their indices are stored in array IFAIL.
• INFO — INTEGER.
  • = 0: successful exit.
  • < 0: if INFO = -i, the i-th argument had an illegal value.
  • > 0: if INFO = i, then i eigenvectors failed to converge in MAXITS iterations. Their indices are stored in array IFAIL.

Internal Parameters 🔥

• MAXITS — INTEGER, default = 5. The maximum number of iterations performed.
• EXTRA — INTEGER, default = 2. The number of iterations performed after norm growth criterion is satisfied, should be at least 1.

Author 🌸

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

Definition at line 172 of file sstein.f.

Author (the auto-generated one) 🦋

Generated automatically by Doxygen for LAPACK from the source code.

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Okay that's the whole page, bestie — LAPACK Version 3.12.0, source SRC/sstein.f(3), and that's the footer tea. Mwah. 💅💖