SRC/dlaexc.f(3)

📦
version 3.12.1 · 7 versions
, in arch rolling

✨ NAME ✨

SRC/dlaexc.f — okay bestie, this is the SRC/dlaexc.f(3) page from the Library Functions Manual, and it’s literally the file/name situation, no extra lore needed 💅

🦋 SYNOPSIS 🦋

🧚 Functions/Subroutines 🧚

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

DLAEXC swaps adjacent diagonal blocks of a real upper quasi-triangular matrix in Schur canonical form, by an orthogonal similarity transformation. Slay, but make it linear algebra 💖

👑 Function/Subroutine Documentation 👑

subroutine dlaexc (logical wantq, integer n, double precision, dimension(
     ldt, * ) t, integer ldt, double precision, dimension( ldq, * ) q,
     integer ldq, integer j1, integer n1, integer n2, double precision,
     dimension( * ) work, integer info)

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

🌸 Purpose 🌸

Okay so here’s the tea 🍓: DLAEXC swaps adjacent diagonal blocks T11 and T22 of order 1 or 2 in an upper quasi-triangular matrix T by an orthogonal similarity transformation.

And the vibe check is real: 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 requirement ✨

🎀 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 DOUBLE PRECISION 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 DOUBLE PRECISION 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 DOUBLE PRECISION 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.
bestie, INFO = 1 is the “not today” outcome 😭 — the blocks are not swapped and T and Q are unchanged. Keep that in mind fr fr.

🫶 Author 🫶

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

Definition at line 136 of file dlaexc.f.

💜 Author 💜

Generated automatically by Doxygen for LAPACK from the source code. Yes, the page itself has author energy twice — iconic, honestly 👑

okay bye bestie 🫶 this was SRC/dlaexc.f(3) from LAPACK Version 3.12.0 — that’s the source/version info on the footer, and it’s giving “manual page but make it cute” 💖✨🎀

📦 where this page comes from