DLAEXC(3)

okay so bestie, welcome to the dlaexc.f(3) page from the LAPACK Library Functions Manual — header path vibe: /home/abui...RC/dlaexc.f(3). This one is a Fortran subroutine page, and it is lowkey a little iconic.

🌸 NAME 🌸

The file being documented is:

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

✨ SYNOPSIS ✨

💖 Functions/Subroutines 💖

Here’s the short signature, no cap:

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

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

🫶 Function/Subroutine Documentation 🫶

Full signature, character for character:

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)

Yep, she’s long. 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.

T must be in Schur canonical form, meaning 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. That’s the whole vibe.

✨ Purpose ✨

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.

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.

🎀 Parameters 🎀

• WANTQ — is LOGICAL. = .TRUE. : accumulate the transformation in the matrix Q; = .FALSE.: do not accumulate the transformation.
• N — is INTEGER. The order of the matrix T. N >= 0.
• 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 — is INTEGER. The leading dimension of the array T. LDT >= max(1,N).
• 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 — is INTEGER. The leading dimension of the array Q. LDQ >= 1; and if WANTQ is .TRUE., LDQ >= N.
• J1 — is INTEGER. The index of the first row of the first block T11.
• N1 — is INTEGER. The order of the first block T11. N1 = 0, 1 or 2.
• N2 — is INTEGER. The order of the second block T22. N2 = 0, 1 or 2.
• WORK — is DOUBLE PRECISION array, dimension (N).
• 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 dlaexc.f.

💅 Author 💅

Generated automatically by Doxygen for LAPACK from the source code.

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okay that’s the whole page, bestie. Footer/source vibe: LAPACK, Version 3.12.0, path /home/abui...RC/dlaexc.f(3). There’s no separate date line in this footer, so I’m not inventing one — periodt. 🫶