SRC/dlaqz2.f(3)

okay so welcome to SRC/dlaqz2.f(3), bestie — this page lives in the Library Functions Manual and it's giving “Fortran subroutine with main character energy.” it chases a little 2x2 shift bulge down one position, and yes, we're keeping every detail. periodt 💅

🌸 NAME 🌸

SRC/dlaqz2.f

that's the name. no notes. 🎀

✨ SYNOPSIS ✨

🎀 Functions/Subroutines 🎀

subroutine dlaqz2 (ilq, ilz, k, istartm, istopm, ihi, a, lda, b, ldb,
           nq, qstart, q, ldq, nz, zstart, z, ldz)

DLAQZ2

📖 Function/Subroutine Documentation 📖

okay here's the full typed signature, copied with love and zero edits:

   subroutine dlaqz2 (logical, intent(in) ilq, logical, intent(in) ilz,
       integer, intent(in) k, integer, intent(in) istartm, integer, intent(in)
       istopm, integer, intent(in) ihi, double precision, dimension( lda, * )
       a, integer, intent(in) lda, double precision, dimension( ldb, * ) b,
       integer, intent(in) ldb, integer, intent(in) nq, integer, intent(in)
       qstart, double precision, dimension( ldq, * ) q, integer, intent(in)
       ldq, integer, intent(in) nz, integer, intent(in) zstart, double
       precision, dimension( ldz,                          * ) z, integer,
       intent(in) ldz)
       DLAQZ2

DLAQZ2

🎯 Purpose 🎯

DLAQZ2 chases a 2x2 shift bulge in a matrix pencil down a single position. that's the whole purpose, and honestly? iconic. 🔥

🧸 Parameters 🧸

• ILQ — ILQ is LOGICAL. Determines whether or not to update the matrix Q. 💖
• ILZ — ILZ is LOGICAL. Determines whether or not to update the matrix Z. 💫
• K — K is INTEGER. Index indicating the position of the bulge. On entry, the bulge is located in (A(k+1:k+2,k:k+1),B(k+1:k+2,k:k+1)). On exit, the bulge is located in (A(k+2:k+3,k+1:k+2),B(k+2:k+3,k+1:k+2)). 👀
• ISTARTM — ISTARTM is INTEGER. that's literally all the source says here, bestie — no extra description, no hidden lore. 🫶
• ISTOPM — ISTOPM is INTEGER. Updates to (A,B) are restricted to (istartm:k+3,k:istopm). It is assumed without checking that istartm <= k+1 and k+2 <= istopm. so yeah, that assumption is doing a lot of heavy lifting 😭
• IHI — IHI is INTEGER. no further description in the source, just integer vibes. 💀
• A — A is DOUBLE PRECISION array, dimension (LDA,N). ⭐
• LDA — LDA is INTEGER. The leading dimension of A as declared in the calling procedure. 🎀
• B — B is DOUBLE PRECISION array, dimension (LDB,N). 🌸
• LDB — LDB is INTEGER. The leading dimension of B as declared in the calling procedure. 🦋
• NQ — NQ is INTEGER. The order of the matrix Q. 👑
• QSTART — QSTART is INTEGER. Start index of the matrix Q. Rotations are applied To columns k+2-qStart:k+4-qStart of Q. (capital T on “To” is in the source, we're keeping it exactly, no cap 👀)
• Q — Q is DOUBLE PRECISION array, dimension (LDQ,NQ). 💜
• LDQ — LDQ is INTEGER. The leading dimension of Q as declared in the calling procedure. ✨
• NZ — NZ is INTEGER. The order of the matrix Z. 🌈
• ZSTART — ZSTART is INTEGER. Start index of the matrix Z. Rotations are applied To columns k+1-qStart:k+3-qStart of Z. (yes, it says qStart in the Z description — copying that exactly too 🫶)
• Z — Z is DOUBLE PRECISION array, dimension (LDZ,NZ). 🍓
• LDZ — LDZ is INTEGER. The leading dimension of Q as declared in the calling procedure. (the source really says Q here, not Z — not me fixing it, just reporting the facts 💀)

🖋️ Author 🖋️

Thijs Steel, KU Leuven 💖

📅 Date 📅

May 2020 🎀

📍 Definition at line 172 of file dlaqz2.f 📍

📜 Author 📜

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 made this SRC/dlaqz2.f(3) page, and the routine is dated May 2020. stay slay, and remember: the bulge is moving down exactly one position 💅💖