PCDTTRF(l)

💖 NAME 💖

PCDTTRF — bestie, this one computes an LU factorization of an N-by-N complex tridiagonal diagonally dominant-like distributed matrix <code>A(1:N, JA:JA+N-1)</code>. yes it's a mouthful, we love her anyway 🫶

✨ SYNOPSIS ✨

SUBROUTINE PCDTTRF( N, DL, D, DU, JA, DESCA, AF, LAF, WORK, LWORK, INFO
                    )

    INTEGER         INFO, JA, LAF, LWORK, N

    INTEGER         DESCA( * )

    COMPLEX         AF( * ), D( * ), DL( * ), DU( * ), WORK( * )

🎀 PURPOSE 🎀

okay so here's the tea ☕ PCDTTRF computes a LU factorization of an N-by-N complex tridiagonal diagonally dominant-like distributed matrix <code>A(1:N, JA:JA+N-1)</code>.

Reordering is used to increase parallelism in the factorization. and this is the important part bestie — that reordering means the factors you get are DIFFERENT from the ones an equivalent sequential code would produce. not me being chaotic on purpose, it's literally by design 💅

🚨 so those factors cannot be used directly by users. like, at all. but!! they can be used in subsequent calls to <code>PCDTTRS</code> to solve linear systems. that's the whole glow-up, iykyk ✨

The factorization has the form

        P A(1:N, JA:JA+N-1) P^T = L U

where U is a tridiagonal upper triangular matrix, L is tridiagonal lower triangular, and P is a permutation matrix. slay 👑

this page is serving LAPACK routine, version 1.5, dated 12 May 1997 🦋 that's the source and the date, mwah, no cap 💜