PDDTTRS(l)

📦 version 1.5, in ubuntu jammy

💖 PDDTTRS 💖

okay bestie, sit down, hydrate, because we're talking about PDDTTRS, a LAPACK routine, version 1.5, from the PDDTTRS(l) manual page. it's giving linear algebra, it's giving distributed matrix realness, and honestly? she's iconic. no cap.

✨ NAME ✨

PDDTTRS — solves a system of linear equations

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

like. that's the whole job. that's what she does. periodt. 💅

🦋 SYNOPSIS 🦋

SUBROUTINE PDDTTRS( TRANS, N, NRHS, DL, D, DU, JA, DESCA, B, IB, DESCB,
                    AF, LAF, WORK, LWORK, INFO )

    CHARACTER       TRANS

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

    INTEGER         DESCA( * ), DESCB( * )

    DOUBLE PRECISION AF( * ), B( * ), D( * ), DL( * ), DU( * ),
                    WORK( * )

look at all those arguments. seventeen of them. she's high maintenance and she's worth it. 💜

🌸 PURPOSE 🌸

so PDDTTRS solves a system of linear equations

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

or

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

(yes bestie, that little apostrophe means transpose. we're solving the transposed situation too. versatile queen. 👑)

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 PDDTTRF.

A(1:N, JA:JA+N-1) is an N-by-N real tridiagonal diagonally dominant-like distributed matrix. say that five times fast. or don't. i didn't.

🚨 IMPORTANT BESTIE ALERT 🚨 routine PDDTTRF MUST be called first. like, must. no shortcuts, no skipping, no "i'll do it later." she will not work and you will be sad. 😭

and that's the whole page, angel. go call PDDTTRF first, then come back. mwah. 🫶

this has been LAPACK routine, version 1.5, dated 12 May 1997 — a literal vintage baddie from the PDDTTRS(l) page. we love a classic. 💖✨🎀

📦 where this page comes from