SRC/chesv_rk.f(3)

🎀 NAME 🎀

Okay bestie, this is the manual page for SRC/chesv_rk.f(3), living inside the Library Functions Manual. It's a LAPACK routine, and it's here to solve linear systems with main-character energy. ✨

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🦋 SYNOPSIS 🦋

🧚 Functions/Subroutines 🧚

subroutine chesv_rk (uplo, n, nrhs, a, lda, e, ipiv, b, ldb, work,
    lwork, info)

CHESV_RK computes the solution to system of linear equations A * X = B for SY matrices. Slay.

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💅 FUNCTION/SUBROUTINE DOCUMENTATION 💅

subroutine chesv_rk (character uplo, integer n, integer nrhs, complex,
    dimension( lda, * ) a, integer lda, complex, dimension( * ) e, integer,
    dimension( * ) ipiv, complex, dimension( ldb, * ) b, integer ldb,
    complex, dimension( * ) work, integer lwork, integer info)

CHESV_RK computes the solution to system of linear equations A * X = B for SY matrices.

🌸 Purpose 🌸

Okay so here's the whole vibe: CHESV_RK computes the solution to a complex system of linear equations A * X = B, where A is an N-by-N Hermitian matrix and X and B are N-by-NRHS matrices. 💖

The bounded Bunch-Kaufman (rook) diagonal pivoting method is used to factor A as:

A = P*U*D*(U**H)*(P**T),  if UPLO = 'U', or
A = P*L*D*(L**H)*(P**T),  if UPLO = 'L',

where U (or L) is unit upper (or lower) triangular matrix, U**H (or L**H) is the conjugate of U (or L), P is a permutation matrix, P**T is the transpose of P, and D is Hermitian and block diagonal with 1-by-1 and 2-by-2 diagonal blocks. No cap, that's the factorization tea. 🫖

CHETRF_RK is called to compute the factorization of a complex Hermitian matrix. The factored form of A is then used to solve the system of equations A * X = B by calling BLAS3 routine CHETRS_3. Periodt. 💅

🎀 Parameters 🎀

• UPLO — UPLO is CHARACTER*1. It specifies whether the upper or lower triangular part of the Hermitian matrix A is stored:
  • = 'U': Upper triangle of A is stored;
  • = 'L': Lower triangle of A is stored.
• N — N is INTEGER. The number of linear equations, i.e., the order of the matrix A. N >= 0.
• NRHS — NRHS is INTEGER. The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.
• A — A is COMPLEX array, dimension (LDA,N). On entry, the Hermitian matrix A.
  • If UPLO = 'U': the leading N-by-N upper triangular part of A contains the upper triangular part of the matrix A, and the strictly lower triangular part of A is not referenced.
  • If UPLO = 'L': the leading N-by-N lower triangular part of A contains the lower triangular part of the matrix A, and the strictly upper triangular part of A is not referenced.

On exit, if INFO = 0, diagonal of the block diagonal matrix D and factors U or L as computed by CHETRF_RK:

• a) ONLY diagonal elements of the Hermitian block diagonal matrix D on the diagonal of A, i.e. D(k,k) = A(k,k); (superdiagonal (or subdiagonal) elements of D are stored on exit 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.

For more info see the description of CHETRF_RK routine.

• LDA — LDA is INTEGER. The leading dimension of the array A. LDA >= max(1,N).
• E — E is COMPLEX array, dimension (N). On exit, contains the output computed by the factorization routine CHETRF_RK, i.e. the superdiagonal (or subdiagonal) elements of the Hermitian 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) is set to 0;
  • If UPLO = 'L': E(i) = D(i+1,i), i=1:N-1, E(N) is set to 0.

💀 NOTE: For 1-by-1 diagonal block D(k), where 1 <= k <= N, the element E(k) is set to 0 in both UPLO = 'U' or UPLO = 'L' cases.

For more info see the description of CHETRF_RK routine.

• IPIV — IPIV is INTEGER array, dimension (N). Details of the interchanges and the block structure of D, as determined by CHETRF_RK.

For more info see the description of CHETRF_RK routine.

• B — B is COMPLEX array, dimension (LDB,NRHS). On entry, the N-by-NRHS right hand side matrix B. On exit, if INFO = 0, the N-by-NRHS solution matrix X.
• LDB — LDB is INTEGER. The leading dimension of the array B. LDB >= max(1,N).
• WORK — WORK is COMPLEX array, dimension ( MAX(1,LWORK) ). Work array used in the factorization stage. On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
• LWORK — LWORK is INTEGER. The length of WORK. LWORK >= 1. For best performance of factorization stage LWORK >= max(1,N*NB), where NB is the optimal blocksize for CHETRF_RK.

If LWORK = -1, then a workspace query is assumed; the routine only calculates the optimal size of the WORK array for factorization stage, 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 = -k, the k-th argument had an illegal value
  • > 0: If INFO = k, the matrix A is singular, because:
    • If UPLO = 'U': column k in the upper triangular part of A contains all zeros.
    • If UPLO = 'L': column k in the lower triangular part of A contains all zeros.

Therefore D(k,k) is exactly zero, and superdiagonal elements of column k of U (or subdiagonal elements of column k of L) are all zeros. The factorization has been completed, but the block diagonal matrix D is exactly singular, and division by zero will occur if it is used to solve a system of equations.

🚨 NOTE: INFO only stores the first occurrence of a singularity, any subsequent occurrence of singularity is not stored in INFO even though the factorization always completes.

💖 Author 💖

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

👑 Contributors: 👑

• December 2016, Igor Kozachenko, Computer Science Division, University of California, Berkeley
• September 2007, Sven Hammarling, Nicholas J. Higham, Craig Lucas, School of Mathematics, University of Manchester

Definition at line 226 of file chesv_rk.f.

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📜 Author 📜

Generated automatically by Doxygen for LAPACK from the source code.

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✨ That's the whole page, bestie. Footer tea: LAPACK, Version 3.12.0, source SRC/chesv_rk.f(3) — no date in the footer, just those deets. Mwah. 💅🎀