SRC/ssptri.f(3)

💅 SRC/ssptri.f(3) — Library Functions Manual ✨

okay bestie, welcome to the SRC/ssptri.f page from the Library Functions Manual. It’s giving “tiny Fortran routine, packed-storage inverse energy,” and we are gonna read it together. 🫶

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🎀 NAME 🎀

SRC/ssptri.f

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✨ SYNOPSIS ✨

🌸 Functions/Subroutines 🌸

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

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🦋 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 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 main character plot, periodt. 👑

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🎀 Parameters 🎀

🌈 UPLO

UPLO is CHARACTER*1. It specifies whether the details of the factorization are stored as an upper or lower triangular matrix.

• = '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. N >= 0.

🦋 AP

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

On entry, 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, 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). Details of the interchanges and the block structure of D as determined by SSPTRF.

🧚 WORK

WORK is REAL array, dimension (N).

👑 INFO

INFO is INTEGER.

• = 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.

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🌸 Author 🌸

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

Definition at line 108 of file ssptri.f.

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💫 Author 💫

Generated automatically by Doxygen for LAPACK from the source code.

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okay that’s the whole page, bestie — footer tea is LAPACK Version 3.12.0 and page SRC/ssptri.f(3). Mwah 💋✨💅