CPTTRF(3)

💖 CPTTRF(3) 💖

okay bestie, welcome to the Library Functions Manual, where today's main character is a .f file with a whole lot of feelings (and by feelings I mean Fortran). This page lives at /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/cpttrf.f and honestly? she's iconic. no cap. 🦋

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✨ NAME ✨

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/cpttrf.f

like, that's her. that's the whole name. it's giving "my parents named me after the street they lived on." 💅

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🌸 SYNOPSIS 🌸

Functions/Subroutines

• subroutine CPTTRF (n, d, e, info) — the one, the only, CPTTRF 💫

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🎀 Function/Subroutine Documentation 🎀

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

CPTTRF. that's it. that's the vibe. 🫶

Purpose:

!>
!> CPTTRF computes the L*D*L**H factorization of a complex Hermitian
!> positive definite tridiagonal matrix A.  The factorization may also
!> be regarded as having the form A = U**H *D*U.
!>

so basically, bestie, she takes your complex Hermitian positive definite tridiagonal matrix A and factors it — either as L*D*L**H or, if you're feeling spicy, as A = U**H *D*U. same energy, different outfit. two ways to slay, pick your fave. ✨ lowkey obsessed with how it just... does both.

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Parameters

• N

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

the order of the matrix A, and she said N >= 0 or nothing. zero is valid, negative is NOT the move. 🙈

• 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**H factorization of A.
!>

a REAL array, dimension (N). on entry she's carrying the n diagonal elements of the tridiagonal matrix A. on exit? glow-up complete — she's now holding the n diagonal elements of the diagonal matrix D from the L*D*L**H factorization of A. she went in one girl and came out another. 💖

• E

!>          E is COMPLEX 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**H factorization of A.
!>          E can also be regarded as the superdiagonal of the unit
!>          bidiagonal factor U from the U**H *D*U factorization of A.
!>

a COMPLEX array, dimension (N-1) — note the N-1, she's a size queen about being exactly one shorter, don't come at her with N. 🙅 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**H factorization of A. and tbh you can also read her as the superdiagonal of the unit bidiagonal factor U from the U**H *D*U factorization of A. dual-threat. main character energy fr fr. 👑

• 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 receipts. an INTEGER, and she has three moods:

• = 0 — successful exit. we love a happy ending. 🎉
• < 0 — if INFO = -k, the k-th argument had an illegal value. someone did NOT read the assignment. 😭
• > 0 — if INFO = k, the leading principal minor of order k is not positive. and here's the nuance bestie, don't skip it: if k < N, the factorization could not be completed, whereas if k = N, the factorization was completed, but D(N) <= 0. two very different "it went wrong" situations and you gotta know which one you're in. 💀

okay but seriously, pay attention to that k < N vs k = N distinction. it's not the same error and treating it like the same error is not it. read the receipt. 🧾

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Author

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

the whole squad. the group chat. absolute legends, every single one. 🫶💜

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Definition at line 91 of file cpttrf.f.

line 91. that's where she lives. remember it. 💅

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⭐ Author ⭐

Generated automatically by Doxygen for LAPACK from the source code. so nobody hand-wrote this — Doxygen just... did that. and honestly? she ate. 🔥

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<aqua>okay that's the whole page bestie, you're basically a LAPACK girlie now.</aqua> 🌈

and finally, the cute little sign-off the manpage gives us: this is LAPACK, Version 3.12.0, from /home/abui...RC/cpttrf.f(3). mwah. 💋✨