SRC/spttrf.f(3)

💖 SRC/spttrf.f 💖

okay so this is SRC/spttrf.f, straight out of the Library Functions Manual, and it’s giving “small but mighty tridiagonal factorization” energy. Let’s break it down, bestie. 💅

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🌸 NAME 🌸

SRC/spttrf.f

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✨ SYNOPSIS ✨

Functions/Subroutines

• subroutine spttrf (n, d, e, info) — SPTTRF

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💅 Function/Subroutine Documentation 💅

subroutine spttrf (integer n, real, dimension( * ) d, real, dimension( * ) e, integer info)

SPTTRF — the subroutine in question, no big deal. 👑

🎀 Purpose 🎀

SPTTRF computes the L*D*L**T factorization of a real symmetric positive definite tridiagonal matrix A. The factorization may also be regarded as having the form A = U**T*D*U. iconic linear algebra behavior, honestly. ✨

🦋 Parameters 🦋

okay bestie, here’s the tea on every single argument:

• N — N is INTEGER. The order of the matrix A. N >= 0.
• D — D is REAL 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.
• E — E is REAL 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*L**T factorization of A. E can also be regarded as the superdiagonal of the unit bidiagonal factor U from the U**T*D*U factorization of A.
• 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.

vibe check: those INFO values are literally the receipts for whether things went okay or absolutely did not. Keep an eye on them. 👀

👑 Author 👑

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

Definition at line 90 of file spttrf.f.

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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Catch you later, bestie — this whole page is SRC/spttrf.f(3) from LAPACK Version 3.12.0. The footer doesn’t list a date, so we’re not inventing one. 💖✨