SRC/dpttrf.f(3)

✨ SRC/dpttrf.f ✨

okay bestie, so this is a Library Functions Manual page for SRC/dpttrf.f — literally one subroutine, and it's a good one. buckle up 💅

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🌸 SYNOPSIS 🌸

Functions/Subroutines

• subroutine dpttrf (n, d, e, info) — the one and only, and the name is literally DPTTRF, periodt.

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🦋 Function/Subroutine Documentation 🦋

subroutine dpttrf (integer n, double precision, dimension( * ) d, double precision, dimension( * ) e, integer info)

yup, that's DPTTRF 🎀

💜 Purpose:

!> !> DPTTRF computes the L*D*LT factorization of a real symmetric !> positive definite tridiagonal matrix A. The factorization may also !> be regarded as having the form A = UT*D*U. !>

so basically it takes your tridiagonal A and breaks it down for you — either as L*D*L**T or as U**T*D*U, same energy, both iconic ✨

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🎀 Parameters

N

!> N is INTEGER !> The order of the matrix A. N >= 0. !>

it's how big A is, and ngl it has to be N >= 0 or we're not doing this 🫶

D

!> D is DOUBLE PRECISION array, dimension (N) !> On entry, the n diagonal elements of the tridiagonal matrix !> A. On exit, the n diagonal elements of the diagonal matrix !> D from the L*D*L**T factorization of A. !>

the glow-up arc of an array 😭 on the way in it's holding the n diagonal elements of the tridiagonal matrix A, and on the way out it's holding the n diagonal elements of the diagonal matrix D from the L*D*L**T factorization of A. main character energy fr fr

E

!> E is DOUBLE PRECISION array, dimension (N-1) !> On entry, the (n-1) subdiagonal elements of the tridiagonal !> matrix A. On exit, the (n-1) subdiagonal elements of the !> unit bidiagonal factor L from the L*D*LT factorization of A. !> E can also be regarded as the superdiagonal of the unit !> bidiagonal factor U from the UT*D*U factorization of A. !>

bestie note the size: dimension (N-1), not N, okay 💀 entering: the (n-1) subdiagonal elements of the tridiagonal matrix A. exiting: the (n-1) subdiagonal elements of the unit bidiagonal factor L from the L*D*L**T factorization of A. and plot twist — E can ALSO be regarded as the superdiagonal of the unit bidiagonal factor U from the U**T*D*U factorization of A. versatile queen 👑

INFO

!> INFO is INTEGER !> = 0: successful exit !> < 0: if INFO = -k, the k-th argument had an illegal value !> > 0: if INFO = k, the leading principal minor of order k !> is not positive; if k < N, the factorization could not !> be completed, while if k = N, the factorization was !> completed, but D(N) <= 0. !>

the vibe check report card 📋

• = 0 — successful exit, we ate, no crumbs 💅
• < 0 — if INFO = -k, the k-th argument had an illegal value 🙈
• > 0 — if INFO = k, the leading principal minor of order k is not positive. if k < N, the factorization could not be completed (😭), while if k = N, the factorization was completed, but D(N) <= 0 (😐 so close bestie)

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👑 Author

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

squad goals, literally 🫶

📍 Definition at line 90 of file dpttrf.f.

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⭐ Author ⭐

Generated automatically by Doxygen for LAPACK from the source code. not me being a whole auto-generated girlie 🤖✨

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heads up bestie: this page is LAPACK 🌈 Version 3.12.0 and it's dated to match — so if you're quoting it in a group chat, cite the version, iykyk 💖

okay that's the whole page, you're welcome, go slay your tridiagonal factorization 🔥🎀