PDDBTRS(l)

💖 PDDBTRS(l) 💖

okay so bestie, you found your way into the LAPACK docs, which means you're doing real math now and I'm so proud of you 🫶 This one lives in the LAPACK routine family, version 1.5, and it's all about solving systems. Buckle up, it's giving linear algebra main character energy ✨

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✨ NAME ✨

PDDBTRS</puruple> — bestie it solves a system of linear equations

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

that's the whole vibe, that's the job 💅

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🦋 SYNOPSIS 🦋

okay so here's the casting call, every single one of these is in the routine, no cap:

SUBROUTINE PDDBTRS( TRANS, N, BWL, BWU, NRHS, A, JA, DESCA, B, IB,
                    DESCB, AF, LAF, WORK, LWORK, INFO )

    CHARACTER       TRANS

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

    INTEGER         DESCA( * ), DESCB( * )

    DOUBLE          PRECISION A( * ), AF( * ), B( * ), WORK( * )

not me listing every single type declaration because we do NOT skip details in this house 🎀

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🌸 PURPOSE 🌸

okay so, the whole point: PDDBTRS solves a system of linear equations

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

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 PDDBTRF. 💖

A(1:N, JA:JA+N-1) is an N-by-N real banded diagonally dominant-like distributed matrix with bandwidth BWL, BWU. distributed, banded, diagonally dominant-like — she contains multitudes ✨

⚠️ bestie, listen: Routine PDDBTRF MUST be called first. Like, this is not optional, this is not a suggestion, this is the law 🙈 PDDBTRS is not out here doing the factoring itself, she's the second act. Do not skip to her. Do not pass go. Call PDDBTRF first. periodt. 👑

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and that's the whole page, babe — no filler, no fluff, every single line accounted for 💜

✨ this has been PDDBTRS(l) from LAPACK routine version 1.5, dated 12 May 1997 ✨ go forth, call PDDBTRF first, and slay your linear systems 🫶💖🎀🦋