DPPTRI(3)

🎀 NAME 🎀

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

okay so this is literally that file bestie, and it lives in the Library Functions Manual (that's the manual name, folder it under that 💅). It's the home of DPPTRI and we're about to get into it ✨

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine DPPTRI (uplo, n, ap, info)

DPPTRI — that's her, that's the icon 👑

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💖 Function/Subroutine Documentation 💖

subroutine DPPTRI (character uplo, integer n, double precision, dimension( * ) ap, integer info)

DPPTRI

Purpose:

!>
!> DPPTRI computes the inverse of a real symmetric positive definite
!> matrix A using the Cholesky factorization A = U**T*U or A = L*L**T
!> computed by DPPTRF.
!>

no cap, she takes your already-Cholesky'd matrix (the one DPPTRF handed you) and flips it into an inverse. main character behavior fr 🔥

Parameters

• UPLO — it's a CHARACTER*1, so it's just one letter and you gotta pick a side:

!>          UPLO is CHARACTER*1
!>          = 'U':  Upper triangular factor is stored in AP;
!>          = 'L':  Lower triangular factor is stored in AP.
!>

• N — an INTEGER, the order of the matrix A. and bestie, N >= 0, no negative nonsense please 🙈

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

• AP — DOUBLE PRECISION array, dimension (N*(N+1)/2). she's packed, she's columnwise, she's a whole linear array doing the most 💅

!>          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
!>          On entry, the triangular factor U or L from the Cholesky
!>          factorization A = U**T*U or A = L*L**T, packed columnwise as
!>          a linear array.  The j-th column of U or L is stored in the
!>          array AP as follows:
!>          if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
!>          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.
!>
!>          On exit, the upper or lower triangle of the (symmetric)
!>          inverse of A, overwriting the input factor U or L.
!>

⚠️ heads up: on exit AP gets overwritten with the upper or lower triangle of the (symmetric) inverse of A. your original factor U or L? gone. she said out with the old 🫶

• INFO — an INTEGER, the vibe check on how it went:

!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument had an illegal value
!>          > 0:  if INFO = i, the (i,i) element of the factor U or L is
!>                zero, and the inverse could not be computed.
!>

like: 0 = slay, < 0 = argument i was illegal (not me...), > 0 = the (i,i) element of the factor U or L is zero so the inverse literally could not be computed 😭 that's the "cannot divide by zero" of it all.

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👑 Author 👑

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

🌸 Definition at line 92 of file dpptri.f. 🌸

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🦋 Author 🦋

Generated automatically by Doxygen for LAPACK from the source code. (yes bestie she was written by a robot, and she ate 💀✨)

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okay so that's the whole page — LAPACK, Version 3.12.0, dated /home/abui...RC/dpptri.f(3) in the header and <rainbow>Version 3.12.0 /home/abui...RC/dpptri.f(3)</rainbow> down at the bottom in the footer 🎀 go forth and invert, ily 🫶💖