PZPTSV(l)

💖 PZPTSV — bestie's guide to solving tridiagonal systems 💖

okay so real talk, this is a LAPACK routine (version 1.5, she's vintage, she's iconic) and she does exactly one thing but she does it flawlessly. no cap.

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✨ NAME ✨

PZPTSV — solves a system of linear equations

A(1:N, JA:JA+N-1) * X = B(IB:IB+N-1, 1:NRHS)

like. that's it. that's her whole job. and she ate. 💅

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🌸 SYNOPSIS 🌸

SUBROUTINE PZPTSV( UPLO, N, NRHS, D, E, JA, DESCA, B, IB, DESCB, WORK,
                   LWORK, INFO )

    CHARACTER      UPLO

    INTEGER        IB, INFO, JA, LWORK, N, NRHS

    INTEGER        DESCA( * ), DESCB( * )

    COMPLEX*16     B( * ), E( * ), WORK( * )

    DOUBLE         PRECISION D( * )

(and yes, that DOUBLE PRECISION is split across two lines like that in the original — we don't touch the code, bestie, we only admire it 🫶)

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🦋 PURPOSE 🦋

okay so here's the tea ☕ — PZPTSV solves a system of linear equations

where A(1:N, JA:JA+N-1) is an N-by-N complex tridiagonal symmetric positive definite distributed matrix. yes, that's a lot of adjectives. she's complex, she's tridiagonal, she's symmetric, she's positive definite, she's distributed. main character energy fr fr 👑

Cholesky factorization is used to factor a reordering of the matrix into L L'. slay.

💡 if you wanna know the details details (and you do, you're nosy, I love that for you), go check out PZPTTRF and PZPTTRS. they're the besties who handle the behind-the-scenes lore.

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🎀 a lil sign-off 🎀

so this was LAPACK routine version 1.5, dated 12 May 1997 — yeah she's older than most of us and still serving 💖. go forth, solve your tridiagonal systems, and remember: the vibe is immaculate, the math is immaculate, and you're doing amazing sweetie. 🌈✨🦋💜