PZPTTRS(l)

✨ PZPTTRS ✨

ok so bestie. welcome to PZPTTRS, a LAPACK routine, version 1.5 era, and she is lowkey the solver of your dreams. she solves a system of linear equations and honestly? she ate. 🎀

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💖 NAME 💖

PZPTTRS — solves a system of linear equations

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

like that's literally her whole job. periodt. 💅

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🌸 SYNOPSIS 🌸

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

    CHARACTER       UPLO

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

    INTEGER         DESCA( * ), DESCB( * )

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

    DOUBLE PRECISION D( * )

ok look at all those arguments. she's thriving. that's a full roster. not one single parameter was left out, no cap. 🫶

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🦋 PURPOSE 🦋

PZPTTRS solves a system of linear equations

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 PZPTTRF.

A(1:N, JA:JA+N-1) is an N-by-N complex tridiagonal symmetric positive definite distributed matrix. yes she said distributed, yes she said tridiagonal, yes she said symmetric positive definite — she contains multitudes 💜

Depending on the value of UPLO, A stores either U or L in the equn

A(1:N, JA:JA+N-1) = U'D *U or L*D L'

as computed by PZPTTRF. so like, whichever letter you picked, she's got you. 🌈

⚠️ bestie listen to me very carefully: Routine PZPTTRF MUST be called first. not "should", not "maybe", not "whenever you feel like it". MUST. do not skip the prequel and then act surprised when everything falls apart. that's on you and not on her. 😭💀

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that's the whole page, queen. no hidden lore, no secret extra flags, she's short and she's perfect and she knows it. ⭐

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✧･ﾟ: ✧･ﾟ: this has been a LAPACK routine, version 1.5, dated 12 May 1997 — slay forever, the girlies stay classic ✧･ﾟ: ✧･ﾟ: 🎀💖