ZTREXC(3)

💅 ztrexc.f — Library Functions Manual 🌸

okay so this is the manpage for ztrexc.f, and it lives at /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/ztrexc.f — yes that's a whole entire path, she's long, she's giving "absolute path realness" 💀 but that's literally the name section, no cap.

It's filed under Library Functions Manual and it's from the LAPACK fam 🫶

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine ZTREXC (compq, n, t, ldt, q, ldq, ifst, ilst, info)

ZTREXC

(that's it, that's the whole synopsis, she's minimal and iconic for it 💅)

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💖 Function/Subroutine Documentation 💖

🦋 the actual signature, look at her:

subroutine ZTREXC (character compq, integer n, complex*16, dimension( ldt, * ) t, integer ldt, complex*16, dimension( ldq, * ) q, integer ldq, integer ifst, integer ilst, integer info)

ZTREXC — say it with me: zee-trex, she reorders stuff, she's the main character 🌟

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🎀 Purpose:

okay so bestie, listen: ZTREXC reorders the Schur factorization of a complex matrix

A = Q*T*Q**H

so that the diagonal element of T with row index IFST is moved to row ILST. literally just a little relocation situation, no biggie ✨

The Schur form T is reordered by a unitary similarity transformation Z**H*T*Z, and optionally the matrix Q of Schur vectors gets updated by postmultiplying it with Z. obsessed with the "optionally" 🫶

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🌈 Parameters

• COMPQ — is CHARACTER*1. the vibe check for whether we touch Q or not:
  • = 'V': update the matrix Q of Schur vectors; — yes queen, update her 👑
  • = 'N': do not update Q. — hands off, leave her alone 🙈
• N — is INTEGER, the order of the matrix T. it must be N >= 0. also, if N == 0 the arguments ILST and IFST may be any value — like, anything, they don't even matter 💀
• T — is COMPLEX*16 array, dimension (LDT,N). On entry: the upper triangular matrix T. On exit: the reordered upper triangular matrix. she goes in triangular, she comes out reordered, that's the whole glow-up ⭐
• LDT — is INTEGER, the leading dimension of the array T. must be LDT >= max(1,N). don't skip this bestie, max(1,N) fr fr 🎀
• Q — is COMPLEX*16 array, dimension (LDQ,N). On entry: if COMPQ = 'V', the matrix Q of Schur vectors. On exit: if COMPQ = 'V', Q has been postmultiplied by the unitary transformation matrix Z which reorders T. If COMPQ = 'N', Q is not referenced — she said don't perceive her 😭
• LDQ — is INTEGER, the leading dimension of the array Q. LDQ >= 1, and if COMPQ = 'V', then LDQ >= max(1,N). conditional queen 💅
• IFST — is INTEGER. that's it. that's the whole description. she's mysterious 🌸
• ILST — is INTEGER. alongside her sister, they specify the reordering of the diagonal elements of T:
  • The element with row index IFST is moved to row ILST by a sequence of transpositions between adjacent elements — adjacent only!! she's a swapper, not a teleporter 🦋
  • 1 <= IFST <= N; 1 <= ILST <= N. — respect the bounds or she'll be upset 👑
• INFO — is INTEGER, the exit-status receipts 📬
  • = 0: successful exit — slay 🎉
  • < 0: if INFO = -i, the i-th argument had an illegal value — somebody misbehaved, and INFO will tell you exactly who 💀

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👑 Author

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

(the whole academic + lab squad, we stan a collaborative effort 🫶)

Definition at line 125 of file ztrexc.f. — line one-two-five, mark it 🎀

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📚 Author (yes, again)

Generated automatically by Doxygen for LAPACK from the source code. — not a human, a robot did this, and honestly? she ate 🤖✨

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and that's the whole page bestie, every flag, every bound, every max(1,N) 💜

LAPACK — Version 3.12.0 — signed, sealed, delivered at /home/abui...RC/ztrexc.f(3), xoxo 💅🎀