SRC/dsytri2.f(3)

okay bestie, welcome to SRC/dsytri2.f(3) from the Library Functions Manual — no cap, we're about to make this LAPACK routine make sense. 💖

🌸 NAME 🌸

SRC/dsytri2.f

✨ SYNOPSIS ✨

🫶 Functions/Subroutines

Here's the group-chat receipt for the callable stuff:

subroutine dsytri2 (uplo, n, a, lda, ipiv, work, lwork, info)
    DSYTRI2

💻 Function/Subroutine Documentation 💻

🌟 subroutine dsytri2 🌟

subroutine dsytri2 (character uplo, integer n, double precision, dimension(
    lda, * ) a, integer lda, integer, dimension( * ) ipiv, double precision,
    dimension( * ) work, integer lwork, integer info)
    DSYTRI2

🎀 Purpose 🎀

okay so the whole point: DSYTRI2 computes the inverse of a DOUBLE PRECISION symmetric indefinite matrix A using the factorization A = U*D*U**T or A = L*D*L**T computed by DSYTRF. DSYTRI2 sets the LEADING DIMENSION of the workspace before calling DSYTRI2X that actually computes the inverse. That's the serve. 💅

🌈 Parameters 🌈

One bullet per parameter, bestie — every value stays exactly as it was:

• UPLO — is CHARACTER*1. It tells you 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 — is INTEGER. The order of the matrix A. N >= 0.
• A — is DOUBLE PRECISION array, dimension (LDA,N). On entry, it's the block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by DSYTRF. On exit, if INFO = 0, it's the (symmetric) inverse of the original matrix. If UPLO = 'U', the upper triangular part of the inverse is formed and the part of A below the diagonal is not referenced; if UPLO = 'L', the lower triangular part of the inverse is formed and the part of A above the diagonal is not referenced. This is the main character transformation arc, literally. ✨
• LDA — is INTEGER. The leading dimension of the array A. LDA >= max(1,N).
• IPIV — is INTEGER array, dimension (N). Details of the interchanges and the block structure of D as determined by DSYTRF.
• WORK — is DOUBLE PRECISION array, dimension (MAX(1,LWORK)).
• LWORK — is INTEGER. The dimension of the array WORK. If N = 0, LWORK >= 1, else LWORK >= (N+NB+1)*(NB+3). If LWORK = -1, then a workspace query is assumed; the routine calculates:
  • the optimal size of the WORK array, returns this value as the first entry of the WORK array,
  • and no error message related to LWORK is issued by XERBLA.
• 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.

💖 Author 💖

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

📍 Definition at line 📍

Definition at line 126 of file dsytri2.f.

👑 Author 👑

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mwah 💋 — this page is from LAPACK, Version 3.12.0, for SRC/dsytri2.f(3). That's the footer, bestie — go compute that inverse and slay. 🫶✨