SRC/dlasy2.f(3)

💅 SRC/dlasy2.f — like, the whole entire manual page, bestie

okay so this is the dlasy2.f page from the LAPACK Library Functions Manual and honestly? it's giving "tiny routine, big brain energy" ✨ stay with me, we're gonna get through it together 🫶

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🌸 SYNOPSIS — Functions/Subroutines

subroutine dlasy2 (ltranl, ltranr, isgn, n1, n2, tl, ldtl, tr, ldtr, b,
    ldb, scale, x, ldx, xnorm, info)

DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2. no cap, that's literally what it does 🔥

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🦋 Function/Subroutine Documentation

subroutine dlasy2 (logical ltranl, logical ltranr, integer isgn, integer n1,
    integer n2, double precision, dimension( ldtl, * ) tl, integer ldtl,
    double precision, dimension( ldtr, * ) tr, integer ldtr, double
    precision, dimension( ldb, * ) b, integer ldb, double precision scale,
    double precision, dimension( ldx, * ) x, integer ldx, double precision
    xnorm, integer info)

DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2. (yes I said it twice, it's iconic, let it have its moment 💅)

🎀 Purpose:

!>
!> DLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in
!>
!>        op(TL)*X + ISGN*X*op(TR) = SCALE*B,
!>
!> where TL is N1 by N1, TR is N2 by N2, B is N1 by N2, and ISGN = 1 or
!> -1.  op(T) = T or T**T, where T**T denotes the transpose of T.
!>

so like. tiny matrices only (1 or 2, periodt), and you're solving for X. that's the vibe 💖

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✨ Parameters ✨

• LTRANL — LTRANL is LOGICAL. on entry, LTRANL specifies the op(TL):

= .FALSE., op(TL) = TL,
= .TRUE., op(TL) = TL**T.

• LTRANR — LTRANR is LOGICAL. on entry, LTRANR specifies the op(TR):

= .FALSE., op(TR) = TR,
= .TRUE., op(TR) = TR**T.

• ISGN — ISGN is INTEGER. on entry, ISGN specifies the sign of the equation as described before. ISGN may only be 1 or -1. 🚨 like, only those two, don't try anything cute 🚨
• N1 — N1 is INTEGER. on entry, N1 specifies the order of matrix TL. N1 may only be 0, 1 or 2. (yes, 0 is allowed, we don't judge 🙈)
• N2 — N2 is INTEGER. on entry, N2 specifies the order of matrix TR. N2 may only be 0, 1 or 2. (same rules, same energy ⭐)
• TL — TL is DOUBLE PRECISION array, dimension (LDTL,2). on entry, TL contains an N1 by N1 matrix. 👑
• LDTL — LDTL is INTEGER. the leading dimension of the matrix TL. LDTL >= max(1,N1).
• TR — TR is DOUBLE PRECISION array, dimension (LDTR,2). on entry, TR contains an N2 by N2 matrix. 🦋
• LDTR — LDTR is INTEGER. the leading dimension of the matrix TR. LDTR >= max(1,N2).
• B — B is DOUBLE PRECISION array, dimension (LDB,2). on entry, the N1 by N2 matrix B contains the right-hand side of the equation. 💖
• LDB — LDB is INTEGER. the leading dimension of the matrix B. LDB >= max(1,N1).
• SCALE — SCALE is DOUBLE PRECISION. on exit, SCALE contains the scale factor. SCALE is chosen less than or equal to 1 to prevent the solution overflowing. 🛟 (it's literally out here protecting X from itself, we stan)
• X — X is DOUBLE PRECISION array, dimension (LDX,2). on exit, X contains the N1 by N2 solution. the main character, fr fr 👑
• LDX — LDX is INTEGER. the leading dimension of the matrix X. LDX >= max(1,N1).
• XNORM — XNORM is DOUBLE PRECISION. on exit, XNORM is the infinity-norm of the solution. 🌈
• INFO — INFO is INTEGER. on exit, INFO is set to:

0: successful exit.
1: TL and TR have too close eigenvalues, so TL or
   TR is perturbed to get a nonsingular equation.

NOTE: In the interests of speed, this routine does not check the inputs for errors. 💀 so like… please check your own inputs bestie, it is NOT gonna do it for you 😭

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🧚 Author

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

Definition at line 172 of file dlasy2.f. 📍

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👑 Author (again, yes)

Generated automatically by Doxygen for LAPACK from the source code. 🤖✨

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and that's the whole entire page, no skips, no cuts, we ate and left absolutely no crumbs 🍓

LAPACK Version 3.12.0 🌸 SRC/dlasy2.f(3) — mwah, go solve something tiny and iconic 💜🫶