SRC/ztrexc.f(3)

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version 3.12.1 · 7 versions
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🌸 NAME 🌸

SRC/ztrexc.f — okay bestie, this is the page for SRC/ztrexc.f(3) from the Library Functions Manual, and it’s giving iconic linear algebra energy 💖

🦋 SYNOPSIS 🦋

✨ Functions/Subroutines ✨

subroutine ztrexc (compq, n, t, ldt, q, ldq, ifst, ilst, info)
           ZTREXC

🎀 Function/Subroutine Documentation 🎀

subroutine ztrexc

subroutine ztrexc (character compq, integer n, complex*16, dimension( ldt, * ) t, integer ldt, complex*16, dimension( ldq, * ) q, integer ldq, integer ifst, integer ilst, integer info)
       ZTREXC

✨ Purpose ✨

So, ZTREXC reorders the Schur factorization of a complex matrix A = Q*T*Q**H, bestie — specifically so that the diagonal element of T with row index IFST is moved to row ILST. 💅

The Schur form T is reordered by a unitary similarity transformation Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by postmultiplying it with Z. Slay.

💖 Parameters 💖

  • COMPQ — this one is CHARACTER*1, no cap:
    • = 'V': update the matrix Q of Schur vectors;
    • = 'N': do not update Q.
  • N — it’s an INTEGER. The order of the matrix T. N >= 0. If N == 0, arguments ILST and IFST may be any value. Periodt.
  • T — a COMPLEX*16 array, dimension (LDT,N). On entry, the upper triangular matrix T. On exit, the reordered upper triangular matrix.
  • LDT — an INTEGER. The leading dimension of the array T. LDT >= max(1,N).
  • Q — a COMPLEX*16 array, dimension (LDQ,N). On entry, if COMPQ = 'V', the matrix Q of Schur vectors. On exit, if COMPQ = 'V', Q has been postmultiplied by the unitary transformation matrix Z which reorders T. If COMPQ = 'N', Q is not referenced.
  • LDQ — an INTEGER. The leading dimension of the array Q. LDQ >= 1, and if COMPQ = 'V', LDQ >= max(1,N).
  • IFST — an INTEGER.
  • ILST — an INTEGER. These two specify the reordering of the diagonal elements of T: the element with row index IFST is moved to row ILST by a sequence of transpositions between adjacent elements. 1 <= IFST <= N; 1 <= ILST <= N.
  • INFO — an 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 125 of file ztrexc.f.

🌈 Author 🌈

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