DSYGS2(3)

DSYGS2(3) 🫶 — Library Functions Manual

okay so bestie, welcome to the DSYGS2(3) page from the Library Functions Manual. This is the LAPACK subroutine that reduces a symmetric definite generalized eigenproblem to standard form using factorization results obtained from spotrf (unblocked algorithm). It’s giving linear algebra main character energy, and yes, we’re getting into every argument. 💅

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NAME

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dsygs2.f

That’s the source-file name for this page. No cap.

SYNOPSIS

Functions/Subroutines ✨

subroutine DSYGS2 (itype, uplo, n, a, lda, b, ldb, info)

DSYGS2 reduces a symmetric definite generalized eigenproblem to standard form, using the factorization results obtained from spotrf (unblocked algorithm).

Function/Subroutine Documentation 💖

subroutine DSYGS2 (integer itype, character uplo, integer n, double precision, dimension( lda, * ) a, integer lda, double precision, dimension( ldb, * ) b, integer ldb, integer info)

DSYGS2 reduces a symmetric definite generalized eigenproblem to standard form, using the factorization results obtained from spotrf (unblocked algorithm).

Purpose 🎀

• DSYGS2 reduces a real symmetric-definite generalized eigenproblem to standard form.
• If ITYPE = 1, the problem is A*x = lambda*B*x, and A is overwritten by inv(U**T)*A*inv(U) or inv(L)*A*inv(L**T).
• 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**T or L**T *A*L.
• B must have been previously factorized as U**T *U or L*L**T by DPOTRF.

Parameters 🌸

• ITYPE — ITYPE is INTEGER; = 1: compute inv(U**T)*A*inv(U) or inv(L)*A*inv(L**T); = 2 or 3: compute U*A*U**T or L**T *A*L.
• UPLO — UPLO is CHARACTER*1; specifies whether the upper or lower triangular part of the symmetric 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 DOUBLE PRECISION array, dimension (LDA,N). On entry, the symmetric 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, the transformed matrix, stored in the same format as A.
• LDA — LDA is INTEGER; the leading dimension of the array A. LDA >= max(1,N).
• B — B is DOUBLE PRECISION array, dimension (LDB,N); the triangular factor from the Cholesky factorization of B, as returned by DPOTRF.
• 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 126 of file dsygs2.f.

Author 📝

Generated automatically by Doxygen for LAPACK from the source code.

From LAPACK Version 3.12.0, footer path /home/abui...RC/dsygs2.f(3) — and there’s no date on this page, bestie, so I’m not making one up 💖