TESTING/EIG/dstect.f(3)

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version 3.12.1 · 2 versions
, in arch rolling

💖 NAME 💖

okay so this page is TESTING/EIG/dstect.f — yes bestie, the whole path is the name — and it lives in the Library Functions Manual. The main character here is DSTECT, a subroutine that counts eigenvalues for a tridiagonal matrix. 💅✨

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine dstect (n, a, b, shift, num)
    DSTECT

🎀 Function/Subroutine Documentation 🎀

Here’s the full signature, served exactly as it is:

subroutine dstect (integer n, double precision, dimension( * ) a, double precision, dimension( * ) b, double precision shift, integer num)

and the name is DSTECT. 🫶

🌸 Purpose 🌸

DSTECT counts the number NUM of eigenvalues of a tridiagonal matrix T which are less than or equal to SHIFT. T has diagonal entries A(1), ... , A(N), and offdiagonal entries B(1), ..., B(N-1).

Also, the source says: see W. Kahan , Report CS41, Computer Science Dept., Stanford University, July 21, 1966. Iconic citation behavior, ngl. 📚💖

🧚 Parameters 🧚

  • N — N is INTEGER. It’s the dimension of the tridiagonal matrix T. 💖
  • A — A is DOUBLE PRECISION array, dimension (N). These are the diagonal entries of the tridiagonal matrix T.
  • B — B is DOUBLE PRECISION array, dimension (N-1). These are the offdiagonal entries of the tridiagonal matrix T.
  • SHIFT — SHIFT is DOUBLE PRECISION. The shift, used as described under Purpose.
  • NUM — NUM is INTEGER. The number of eigenvalues of T less than or equal to SHIFT.

💜 Author 💜

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

Definition at line 81 of file dstect.f. 🫶

💜 Author 💜

Generated automatically by Doxygen for LAPACK from the source code.

xoxo, this baddie is from TESTING/EIG/dstect.f(3), LAPACK Version 3.12.0 💖✨🎀

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