SSPTRI(3)

📦 version 3.12.0, in opensuse-leap 16.0

🎀 NAME 🎀

Header vibes: /home/abui...RC/ssptri.f(3) + Library Functions Manual + /home/abui...RC/ssptri.f(3) — yes bestie, the path shows up twice and we’re keeping it exactly like that 💅.

The actual source path is /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/ssptri.f.

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine SSPTRI (uplo, n, ap, ipiv, work, info)
    SSPTRI

💅 Function/Subroutine Documentation 💅

🫶 subroutine SSPTRI (...)

subroutine SSPTRI (character uplo, integer n, real, dimension( * ) ap,
       integer, dimension( * ) ipiv, real, dimension( * ) work, integer info)
       SSPTRI

🌸 Purpose 🌸

Okay so picture this: SSPTRI computes the inverse of a real symmetric indefinite matrix A in packed storage using the factorization A = U*D*U**T or A = L*D*L**T computed by SSPTRF. That’s the whole purpose, and honestly? iconic. ✨

🍓 Parameters 🍓

UPLO

UPLO is CHARACTER*1 and it specifies whether the details of the factorization are stored as an upper or lower triangular matrix. The values are:

  • = 'U': Upper triangular, form is A = U*D*U**T;
  • = 'L': Lower triangular, form is A = L*D*L**T.

N

N is INTEGER — the order of the matrix A. Constraint: N >= 0. 🫶

AP

AP is REAL array, dimension (N*(N+1)/2).

On entry, it holds the block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by SSPTRF, stored as a packed triangular matrix.

On exit, if INFO = 0, it holds the (symmetric) inverse of the original matrix, stored as a packed triangular matrix. The j-th column of inv(A) is stored in the array AP as follows:

  • if UPLO = 'U', AP(i + (j-1)*j/2) = inv(A)(i,j) for 1<=i<=j;
  • if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.

IPIV

IPIV is INTEGER array, dimension (N). It carries the details of the interchanges and the block structure of D as determined by SSPTRF. Simple. 💅

WORK

WORK is REAL array, dimension (N). That’s it — just workspace, no drama. 🌸

INFO

INFO is INTEGER, and it reports:

  • = 0: successful exit
  • < 0: if INFO = -i, the i-th argument had an illegal value
  • > 0: if INFO = i, D(i,i) = 0; the matrix is singular and its inverse could not be computed.
Singular matrix alert: if INFO > 0, the inverse could not be computed. Not the vibe, but important. 💀

👑 Author 👑

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

🌈 Definition at line 108 of file ssptri.f 🌈

Definition at line 108 of file ssptri.f.

🧚 Author 🧚

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That’s the page, bestie! Footer sign-off: LAPACK, Version 3.12.0, page /home/abui...RC/ssptri.f(3). There’s no date listed in the footer, so I’m not making one up — we respect the source code in this house. 💖🫶✨

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