CGTTS2(3)

🌸 NAME 🌸

ok so bestie, this page is literally all about /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/cgtts2.f — and yes, it's from the Library Functions Manual (the header up top literally reads /home/abui...RC/cgtts2.f(3), no cap). It's a Fortran source file that's giving main character energy in LAPACK's SRC folder. 💅

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine CGTTS2 (itrans, n, nrhs, dl, d, du, du2, ipiv, b, ldb)

so what does it do? CGTTS2 solves a system of linear equations with a tridiagonal matrix using the LU factorization computed by sgttrf. that's the whole vibe fr fr 🫶

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🎀 Function/Subroutine Documentation 🎀

subroutine CGTTS2 (integer itrans, integer n, integer nrhs, complex,
    dimension( * ) dl, complex, dimension( * ) d, complex, dimension( * )
    du, complex, dimension( * ) du2, integer, dimension( * ) ipiv, complex,
    dimension( ldb, * ) b, integer ldb)

CGTTS2 solves a system of linear equations with a tridiagonal matrix using the LU factorization computed by sgttrf. (yes that's exactly what the page says, we're not editing the lore 👑)

🌈 Purpose:

!>
!> CGTTS2 solves one of the systems of equations
!>    A * X = B,  A**T * X = B,  or  A**H * X = B,
!> with a tridiagonal matrix A using the LU factorization computed
!> by CGTTRF.
!>

so it's picking one of three equations to solve depending on the transpose situation. iconic behavior honestly ✨

💖 Parameters 💖

• ITRANS — bestie this one is an INTEGER, and it tells you which form of the system of equations you're dealing with:
  • = 0: A * X = B (No transpose)
  • = 1: A**T * X = B (Transpose)
  • = 2: A**H * X = B (Conjugate transpose)

iykyk 💅

• N — an INTEGER. it's the order of the matrix A. that's it, that's the whole thing 🦋
• NRHS — an INTEGER. the number of right hand sides, i.e., the number of columns of the matrix B. and listen: NRHS >= 0. respect the boundary bestie 🙈
• DL — a COMPLEX array, dimension (N-1). these are the (n-1) multipliers that define the matrix L from the LU factorization of A. lowkey the backbone of the whole operation 💀
• D — a COMPLEX array, dimension (N). the n diagonal elements of the upper triangular matrix U from the LU factorization of A. main diagonal energy ⭐
• DU — a COMPLEX array, dimension (N-1). the (n-1) elements of the first super-diagonal of U. slay, super-diagonal 🎀
• DU2 — a COMPLEX array, dimension (N-2). the (n-2) elements of the second super-diagonal of U. (note the N-2 bestie, not N-1, we stay accurate here 💅)
• IPIV — an INTEGER array, dimension (N). the pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIV(i). IPIV(i) will always be either i or i+1; IPIV(i) = i indicates a row interchange was not required. so basically it's the receipts of who swapped with who 👑
• B — a COMPLEX array, dimension (LDB,NRHS). on entry, the matrix of right hand side vectors B. on exit, B is overwritten by the solution vectors X. not me gaslighting your array… it literally gets overwritten bestie 😭
• LDB — an INTEGER. the leading dimension of the array B. and LDB >= max(1,N). mandatory, no negotiating 🌸

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🧚 Author 🧚

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

definition at line 127 of file cgtts2.f. noted for the record 📌

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💜 Author 💜

Generated automatically by Doxygen for LAPACK from the source code. so nobody hand-wrote this one, it's a bot's finest work 🤖✨

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okay that's the whole page bestie, you're officially fluent in CGTTS2 now 🫶💖 stay hydrated, keep your LDB >= max(1,N), and remember — this was all brought to you by LAPACK, Version 3.12.0, source file /home/abui...RC/cgtts2.f(3). periodt. 💅🌸