CHEGS2(3)

🎀 NAME 🎀

okay bestie, this is the page for chegs2.f(3) from the LAPACK Library Functions Manual ✨. The source file it’s talking about is:

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/chegs2.f

🌸 SYNOPSIS 🌸

Functions/Subroutines 💅

subroutine CHEGS2 (itype, uplo, n, a, lda, b, ldb, info)

CHEGS2 reduces a Hermitian definite generalized eigenproblem to standard form, using the factorization results obtained from cpotrf (unblocked algorithm). No cap, that’s the whole vibe.

💖 Function/Subroutine Documentation 💖

🦋 subroutine CHEGS2 🦋

subroutine CHEGS2 (integer itype, character uplo, integer n, complex, dimension( lda, * ) a, integer lda, complex, dimension( ldb, * ) b, integer ldb, integer info)

CHEGS2 reduces a Hermitian definite generalized eigenproblem to standard form, using the factorization results obtained from cpotrf (unblocked algorithm). It’s giving “unblocked algorithm” main character energy 👑

✨ Purpose ✨

CHEGS2 reduces a complex Hermitian-definite generalized eigenproblem to standard form. Periodt.

• If ITYPE = 1, the problem is A*x = lambda*B*x, and A is overwritten by inv(U**H)*A*inv(U) or inv(L)*A*inv(L**H).
• If ITYPE = 2 or 3, the problem is A*B*x = lambda*x or B*A*x = lambda*x, and A is overwritten by U*A*U**H or L**H *A*L.

lowkey important: B must have been previously factorized as U**H *U or L*L**H by ZPOTRF. That’s not optional, bestie 🫶

🧚 Parameters 🧚

• ITYPE — ITYPE is INTEGER
  • = 1: compute inv(U**H)*A*inv(U) or inv(L)*A*inv(L**H);
  • = 2 or 3: compute U*A*U**H or L**H *A*L.
• UPLO — UPLO is CHARACTER*1. It says whether the upper or lower triangular part of the Hermitian matrix A is stored, and how B has been factorized.
  • = 'U': Upper triangular
  • = 'L': Lower triangular
• N — N is INTEGER. The order of the matrices A and B. N >= 0.
• A — A is COMPLEX array, dimension (LDA,N). On entry, it’s 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, this is the transformed matrix, stored in the same format as A. Slay 💅
• LDA — LDA is INTEGER. The leading dimension of the array A. LDA >= max(1,N).
• B — B is COMPLEX array, dimension (LDB,N). This is the triangular factor from the Cholesky factorization of B, as returned by CPOTRF. B is modified by the routine but restored on exit. Cute of it, honestly 🎀
• LDB — LDB is INTEGER. The leading dimension of the array B. LDB >= max(1,N).
• INFO — INFO is INTEGER.
  • = 0: successful exit.
  • < 0: if INFO = -i, the i-th argument had an illegal value.

👑 Author 👑

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

Definition at line 127 of file chegs2.f.

🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code.

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okay that’s the whole page, bestie 💖. Cute sign-off: this footer energy is LAPACK Version 3.12.0 and /home/abui...RC/chegs2.f(3). Byeee 👋✨