PDPTTRS(l)

💖 PDPTTRS 💖

okay bestie, welcome to the LAPACK cinematic universe, this one is PDPTTRS, and she is a solver. 🫶

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✨ NAME ✨

PDPTTRS</p> — solves a system of linear equations that looks like this:

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

that's it. that's the whole vibe. 💅

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🌸 SYNOPSIS 🌸

SUBROUTINE PDPTTRS( N, NRHS, D, E, JA, DESCA, B, IB, DESCB, AF, LAF,
                    WORK, LWORK, INFO )

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

    INTEGER         DESCA( * ), DESCB( * )

    DOUBLE          PRECISION AF( * ), B( * ), D( * ), E( * ), WORK( * )

look at all those arguments. she's got range. 👑

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🦋 PURPOSE 🦋

so like, PDPTTRS solves a system of linear equations, right?

where A(1:N, JA:JA+N-1) is the matrix used to produce the factors stored in A(1:N,JA:JA+N-1) and AF by PDPTTRF.

and like, A(1:N, JA:JA+N-1) is an N-by-N real tridiagonal symmetric positive definite distributed matrix. yes that is a lot of adjectives, she's just built like that. tridiagonal! symmetric! positive definite! distributed! main character energy fr fr. 🌈

⚠️ bestie listen to me. routine PDPTTRF MUST be called first. like, MUST must. no skipping. no shortcuts. the vibes will simply not be there if you don't. 🚨

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okay and that's literally the whole page, she's a short one but she's iconic. ✨

this was the LAPACK routine, version 1.5, dated 12 May 1997 — yes she's an older queen but she ATE and she's still serving. 💀💖 byeee, go call PDPTTRF first, ily 🎀🦋