SRC/sgttrf.f(3)

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version 3.12.1 · 4 versions
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💖 SRC/sgttrf.f 💖

okay bestie, this page is from the Library Functions Manual, and it's all about SGTTRF — the tridiagonal LU factorization girlie. every flag, array, and “what happens on exit” detail is down below, no cap 💅

🌸 NAME 🌸

SRC/sgttrf.f

✨ SYNOPSIS ✨

🎀 Functions/Subroutines 🎀

subroutine sgttrf (n, dl, d, du, du2, ipiv, info)

SGTTRF

💅 Function/Subroutine Documentation 💅

🫶 subroutine sgttrf 🫶

subroutine sgttrf (integer n, real, dimension( * ) dl, real, dimension( * )
d, real, dimension( * ) du, real, dimension( * ) du2, integer,
dimension( * ) ipiv, integer info)

SGTTRF

🦋 Purpose 🦋

SGTTRF computes an LU factorization of a real tridiagonal matrix A using elimination with partial pivoting and row interchanges. periodt.

The factorization has the form

A = L * U

where L is a product of permutation and unit lower bidiagonal matrices and U is upper triangular with nonzeros in only the main diagonal and first two superdiagonals. iconic behavior, honestly.

🌈 Parameters 🌈

  • N — N is INTEGER. the order of the matrix A.
  • DL — DL is REAL array, dimension (N-1). on entry, DL must contain the (n-1) sub-diagonal elements of A.

on exit, DL is overwritten by the (n-1) multipliers that define the matrix L from the LU factorization of A. she gets a whole new identity, lowkey.

  • D — D is REAL array, dimension (N). on entry, D must contain the diagonal elements of A.

on exit, D is overwritten by the n diagonal elements of the upper triangular matrix U from the LU factorization of A. slay.

  • DU — DU is REAL array, dimension (N-1). on entry, DU must contain the (n-1) super-diagonal elements of A.

on exit, DU is overwritten by the (n-1) elements of the first super-diagonal of U. main character energy.

  • DU2 — DU2 is REAL array, dimension (N-2). on exit, DU2 is overwritten by the (n-2) elements of the second super-diagonal of U.
  • IPIV — IPIV is INTEGER array, dimension (N). the pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIV(i). IPIV(i) will always be either i or i+1; IPIV(i) = i indicates a row interchange was not required. very “know your row-swap receipts” of it.
  • INFO — INFO is INTEGER.
    • = 0: successful exit ✨
    • < 0: if INFO = -k, the k-th argument had an illegal value 😭
    • > 0: if INFO = k, U(k,k) is exactly zero. the factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations. this is the “bestie, do NOT divide by zero” warning fr fr 💀

👑 Author 👑

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 123 of file sgttrf.f.

🧚 Author 🧚

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okay that's the whole page, bestie 🫶✨ this cutie was brought to you by LAPACK, Version 3.12.0, and the source is SRC/sgttrf.f(3) 💖🎀🦋

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