SRC/csytri_3.f(3)

💖 SRC/csytri_3.f 💖

okay bestie, this is the Library Functions Manual page for SRC/csytri_3.f(3), and it’s giving “I do linear algebra and I do it fabulously.” 💅✨

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✨ NAME ✨

• SRC/csytri_3.f

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✨ SYNOPSIS ✨

🫶 Functions/Subroutines 🫶

• subroutine csytri_3 (uplo, n, a, lda, e, ipiv, work, lwork, info) — CSYTRI_3

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💅 Function/Subroutine Documentation 💅

🌸 subroutine csytri_3 🌸

subroutine csytri_3 (character uplo, integer n, complex, dimension( lda, * )
       a, integer lda, complex, dimension( * ) e, integer, dimension( * ) ipiv,
       complex, dimension( * ) work, integer lwork, integer info)

CSYTRI_3

🎀 Purpose 🎀

okay so, CSYTRI_3 computes the inverse of a complex symmetric indefinite matrix A using the factorization computed by CSYTRF_RK or CSYTRF_BK:

A = P*U*D*(U**T)*(P**T) or A = P*L*D*(L**T)*(P**T),

where U (or L) is unit upper (or lower) triangular matrix, U**T (or L**T) is the transpose of U (or L), P is a permutation matrix, P**T is the transpose of P, and D is symmetric and block diagonal with 1-by-1 and 2-by-2 diagonal blocks.

CSYTRI_3 sets the leading dimension of the workspace before calling CSYTRI_3X that actually computes the inverse. This is the blocked version of the algorithm, calling Level 3 BLAS. ✨

💜 Parameters 💜

• UPLO UPLO is CHARACTER*1. Specifies whether the details of the factorization are stored as an upper or lower triangular matrix.
  • = 'U': Upper triangle of A is stored;
  • = 'L': Lower triangle of A is stored.
• N N is INTEGER. The order of the matrix A. N >= 0.
• A A is COMPLEX array, dimension (LDA,N). On entry, diagonal of the block diagonal matrix D and factors U or L as computed by CSYTRF_RK and CSYTRF_BK:
  • a) ONLY diagonal elements of the symmetric block diagonal matrix D on the diagonal of A, i.e. D(k,k) = A(k,k); (superdiagonal (or subdiagonal) elements of D should be provided on entry in array E), and
  • b) If UPLO = 'U': factor U in the superdiagonal part of A. If UPLO = 'L': factor L in the subdiagonal part of A.

On exit, if INFO = 0, 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.

• LDA LDA is INTEGER. The leading dimension of the array A. LDA >= max(1,N).
• E E is COMPLEX array, dimension (N). On entry, contains the superdiagonal (or subdiagonal) elements of the symmetric block diagonal matrix D with 1-by-1 or 2-by-2 diagonal blocks, where If UPLO = 'U': E(i) = D(i-1,i),i=2:N, E(1) not referenced; If UPLO = 'L': E(i) = D(i+1,i),i=1:N-1, E(N) not referenced.

NOTE: For 1-by-1 diagonal block D(k), where 1 <= k <= N, the element E(k) is not referenced in both UPLO = 'U' or UPLO = 'L' cases.

• IPIV IPIV is INTEGER array, dimension (N). Details of the interchanges and the block structure of D as determined by CSYTRF_RK or CSYTRF_BK.
• WORK WORK is COMPLEX array, dimension (N+NB+1)*(NB+3). On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
• LWORK LWORK is INTEGER. The length of WORK. LWORK >= (N+NB+1)*(NB+3).

okay bestie, important note: if LDWORK = -1, then a workspace query is assumed; the routine only calculates the optimal size of 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 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.

🦋 Contributors 🦋

• November 2017, Igor Kozachenko, Computer Science Division, University of California, Berkeley

⭐ Definition at line 168 of file csytri_3.f. ⭐

🧚 Author 🧚

Generated automatically by Doxygen for LAPACK from the source code.

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