SLASRT2(l)

📦 version 1.5, in ubuntu jammy

💖 SLASRT2 💖 — the LAPACK routine bestie

okay so this is SLASRT2, a LAPACK routine, and she's literally just here to put your numbers in order. Version 1.5 energy. Let's get into it, no cap.

✨ NAME ✨

SLASRT2 — sorts the numbers in D in increasing order (if ID = 'I') or in decreasing order (if ID = 'D'). That's it. That's the whole job. She's an icon, she's a legend, and she's the moment. 👑

🦋 SYNOPSIS 🦋

SUBROUTINE SLASRT2( ID, N, D, KEY, INFO )

    CHARACTER       ID

    INTEGER         INFO, N

    INTEGER         KEY( * )

    REAL            D( * )

the way that she takes five arguments and one of them is literally just a single character telling her which way to go. main character energy fr fr. 💅

🌸 PURPOSE 🌸

Sort the numbers in D in increasing order (if ID = 'I') or in decreasing order (if ID = 'D').

She uses Quick Sort, but — and this is the cute part — she reverts to Insertion sort on arrays of size <= 20. tiny arrays deserve gentle treatment, periodt. 🧚

The dimension of STACK limits N to about 2**32. so like, enormous, but not infinite, bestie. know your limits. 💀

🎀 ARGUMENTS 🎀

  • ID (input) CHARACTER*1 — the vibe selector:
    • = 'I': sort D in increasing order;
    • = 'D': sort D in decreasing order.
  • N (input) INTEGER — the length of the array D. how many little guys are we sorting. 🔢
  • D (input/output) REAL array, dimension (N) — on entry, the array to be sorted. On exit, D has been sorted into increasing order (D(1) <= ... <= D(N)) or into decreasing order (D(1) >= ... >= D(N)), depending on ID. she comes in messy and leaves immaculate. glow-up of the century. ✨
  • KEY (input/output) INTEGER array, dimension (N) — on entry, KEY contains a key to each of the entries in D(). Typically, KEY(I) = I for all I. On exit, KEY is permuted in exactly the same manner as D() was permuted from input to output. Therefore, if KEY(I) = I for all I upon input, then D_out(I) = D_in(KEY(I)). 🫶
not me explaining this like a group chat receipt: KEY tags along with D through the exact same shuffling, so you can always trace every sorted number back to where it started. no number gets lost, everyone gets home safe. 🙈
  • INFO (output) INTEGER — the status report:
    • = 0: successful exit 🎉 slay.
    • < 0: if INFO = -i, the i-th argument had an illegal value. bestie noooo one of your arguments is not it. 😭
⚠️ heads up: INFO < 0 means an argument was illegal — check which one with -i before you blame the algorithm, okay? she's not the problem. 💅

and that's the whole page! this was the SLASRT2(l) manual page from LAPACK version 1.5, dated 12 May 1997. yes she's vintage, yes she still eats, we love a classic. bye bestie, go sort something. 💖🌈⭐

📦 where this page comes from