SRC/slaexc.f(3)

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version 3.12.1 · 7 versions
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hey bestie, welcome to SRC/slaexc.f(3) from the Library Functions Manual 💅 this page is giving LAPACK subroutine energy, and the subroutine is slaexc.

✨ NAME ✨

SRC/slaexc.f — the file/page name, periodt. It’s the docs for slaexc, which swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation. 🦋

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine slaexc (wantq, n, t, ldt, q, ldq, j1, n1, n2, work, info)

SLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation. ✨

✨ Function/Subroutine Documentation ✨

subroutine slaexc (logical wantq, integer n, real, dimension( ldt, * ) t,
       integer ldt, real, dimension( ldq, * ) q, integer ldq, integer j1,
       integer n1, integer n2, real, dimension( * ) work, integer info)

SLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation.

Purpose: ✨

okay so the purpose is literally this: SLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in an upper quasi-triangular matrix T by an orthogonal similarity transformation. 🔥

T must be in Schur canonical form, that is, block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each 2-by-2 diagonal block has its diagonal elements equal and its off-diagonal elements of opposite sign. No cap, that’s the rule. 👑

Parameters

  • WANTQ — WANTQ is LOGICAL; = .TRUE. : accumulate the transformation in the matrix Q; = .FALSE.: do not accumulate the transformation. 💖
  • N — N is INTEGER; the order of the matrix T. N >= 0.
  • T — T is REAL array, dimension (LDT,N); On entry, the upper quasi-triangular matrix T, in Schur canonical form. On exit, the updated matrix T, again in Schur canonical form. 🎀
  • LDT — LDT is INTEGER; the leading dimension of the array T. LDT >= max(1,N).
  • Q — Q is REAL array, dimension (LDQ,N); On entry, if WANTQ is .TRUE., the orthogonal matrix Q. On exit, if WANTQ is .TRUE., the updated matrix Q. If WANTQ is .FALSE., Q is not referenced. 🌸
  • LDQ — LDQ is INTEGER; the leading dimension of the array Q. LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N.
  • J1 — J1 is INTEGER; the index of the first row of the first block T11.
  • N1 — N1 is INTEGER; the order of the first block T11. N1 = 0, 1 or 2.
  • N2 — N2 is INTEGER; the order of the second block T22. N2 = 0, 1 or 2. 🦋
  • WORK — WORK is REAL array, dimension (N).
  • INFO — INFO is INTEGER; = 0: successful exit; = 1: the transformed matrix T would be too far from Schur form; the blocks are not swapped and T and Q are unchanged. 💀

Author

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

Definition at line 136 of file slaexc.f.

✨ Author ✨

Generated automatically by Doxygen for LAPACK from the source code.

That’s the whole page, bestie — the sign-off vibes are LAPACK Version 3.12.0 and page SRC/slaexc.f(3), with no date printed, iykyk 🫶✨

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