ZUNGTR(3)

💅 ZUNGTR(3) — the group-chat edition 💅

okay so bestie, welcome to the zungtr.f(3) page from the Library Functions Manual. This is the one that builds a complex unitary matrix Q out of elementary reflectors from ZHETRD, and yes it's giving main-character linear algebra energy. 🦋

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🌸 NAME 🌸

The NAME situation is literally this path:

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

That's the whole NAME, no cap. 💖

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✨ SYNOPSIS ✨

Functions/Subroutines

subroutine ZUNGTR (uplo, n, a, lda, tau, work, lwork, info)
           ZUNGTR

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🎀 Function/Subroutine Documentation 🎀

Here's the full signature, copied exactly so nobody comes for me:

   subroutine ZUNGTR (character uplo, integer n, complex*16, dimension( lda, *
       ) a, integer lda, complex*16, dimension( * ) tau, complex*16, dimension(
       * ) work, integer lwork, integer info)
       ZUNGTR

💖 Purpose 💖

okay so ZUNGTR generates a complex unitary matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by ZHETRD:

if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),

if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).

Periodt. That's the whole purpose. 🌈

🌟 Parameters 🌟

• UPLO — UPLO is CHARACTER*1.
  • = 'U': Upper triangle of A contains elementary reflectors from ZHETRD;
  • = 'L': Lower triangle of A contains elementary reflectors from ZHETRD.
• N — N is INTEGER. It's the order of the matrix Q. N >= 0.
• A — A is COMPLEX*16 array, dimension (LDA,N). On entry, the vectors which define the elementary reflectors, as returned by ZHETRD. On exit, the N-by-N unitary matrix Q.
• LDA — LDA is INTEGER. The leading dimension of the array A. LDA >= N.
• TAU — TAU is COMPLEX*16 array, dimension (N-1). TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by ZHETRD.
• WORK — WORK is COMPLEX*16 array, dimension (MAX(1,LWORK)). On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
• LWORK — LWORK is INTEGER. The dimension of the array WORK. LWORK >= N-1. For optimum performance LWORK >= (N-1)*NB, where NB is the optimal blocksize.

If LWORK = -1, then a workspace query is assumed; the routine only 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 — 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 122 of file zungtr.f.

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🫶 Author 🫶

Generated automatically by Doxygen for LAPACK from the source code.

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okay bestie, cute sign-off time: LAPACK Version 3.12.0, footer source path /home/abui...RC/zungtr.f(3), and no separate date is printed in the original footer — so I'm not inventing one. 💖✨