lis_esolve(3f)

💖 lis_esolve(3f) 💖

okay bestie, so this is a page from the Lis Library Functions manual, and it's all about lis_esolve — the little routine that makes eigenvalues happen. it lives in section 3f, so it's a Fortran-callable library joint. let's get into it 🦋

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✨ NAME ✨

lis_esolve — solve the standard eigenvalue problem. that's it, that's the whole job. she's focused, she's got one task, and she slays it. 💅

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✨ SYNOPSIS ✨

subroutine lis_esolve(LIS_MATRIX A, LIS_VECTOR x, LIS_REAL evalue,
LIS_ESOLVER esolver, LIS_INTEGER ierr);

five arguments, one subroutine, zero drama (well, mostly — ierr is there in case things get messy 😭). keep this signature exactly as written, no cap.

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✨ DESCRIPTION ✨

so basically? she solves the standard eigenvalue problem:

Ax = lx

...using whatever eigensolver you hand her. you pick the esolver, she does the math, you get your eigenvalue and your eigenvector. it's giving main character energy ✨

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✨ INPUT ✨

here's what you gotta pass in, bestie:

• A — the coefficient matrix. the whole reason we're here. 💖
• x — the initial vector. your starting vibe, she takes it from there.
• esolver — the esolver. yes, the argument is literally named "the esolver" and described as "the esolver." iconic, honestly. 🎀

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✨ OUTPUT ✨

and here's what comes back out:

• evalue — the eigenvalue of mode 0. that's the one you asked for. 👑
• x — the associated eigenvector. she's the partner-in-crime to that eigenvalue. 🫶
• esolver — the number of iterations, the execution time, etc. all the receipts. the stats. the data. ⭐

heads up: x and esolver show up in both INPUT and OUTPUT — they go in, and they get updated coming out. and ierr from the synopsis? that's your error code situation, so check it, bestie, fr fr. 🙈

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✨ SEE ALSO ✨

• lis(3) — the mothership manpage, go read her next 🌸
• http://www.ssisc.org/lis/ — the website, for all your Lis needs 🧚

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and that's the whole page!! no cap, you're now a lis_esolve expert 🍓

Man Page · 23 Oct 2016 · lis_esolve(3f) — mwah, love u, go solve some eigenvalues 💜✨