PSDTTRS(l)

✨ PSDTTRS(l) ✨

okay bestie, welcome to the LAPACK corner of the group chat 💖 this one is PSDTTRS, a routine from LAPACK version 1.5, and she is here to solve linear systems for you. no cap. 🫶

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🌸 NAME 🌸

PSDTTRS — solve a system of linear equations

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

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🎀 SYNOPSIS 🎀

SUBROUTINE PSDTTRS( 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( * )

    REAL            AF( * ), B( * ), D( * ), DL( * ), DU( * ), WORK( * )

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🦋 PURPOSE 🦋

so like, PSDTTRS solves a system of linear equations, and it's giving two flavours 👑

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)

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 PSDTTRF.

A(1:N, JA:JA+N-1) is an N-by-N real tridiagonal diagonally dominant-like distributed matrix. lowkey a mouthful, but that's the vibe. ✨

💀 not me reminding you again but: routine PSDTTRF MUST be called first. like, MUST MUST. the factors gotta exist before you go solving anything, bestie. main character energy requires setup. 🔥

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and that's the whole page, periodt 💅 this was PSDTTRS(l) from LAPACK version 1.5, dated 12 May 1997 — iconic behaviour, honestly, she's been slaying since the nineties and she's still not tired 👑🌺 bye bestie, go solve something 🦋💖