SRC/dlaeda.f(3)

okay so bestie, welcome to SRC/dlaeda.f(3) from the Library Functions Manual — yes, we're doing Fortran LAPACK lore today and it's giving iconic 💅✨

🌸 NAME 🌸

SRC/dlaeda.f — that's the name, no cap. This page is serving the dlaeda subroutine and its whole argument friend group 💖.

✨ SYNOPSIS ✨

🧚 Functions/Subroutines 🧚

       subroutine dlaeda (n, tlvls, curlvl, curpbm, prmptr, perm, givptr,
           givcol, givnum, q, qptr, z, ztemp, info)
           DLAEDA used by DSTEDC. Computes the Z vector determining the rank-
           one modification of the diagonal matrix. Used when the original
           matrix is dense.

Short version: this is the dlaeda subroutine and its entire argument roster. We're gonna meet every single one, don't worry 🫶.

🌀 Function/Subroutine Documentation 🌀

       subroutine dlaeda (integer n, integer tlvls, integer curlvl, integer curpbm,
           integer, dimension( * ) prmptr, integer, dimension( * ) perm, integer,
           dimension( * ) givptr, integer, dimension( 2, * ) givcol, double
           precision, dimension( 2, * ) givnum, double precision, dimension( * ) q,
           integer, dimension( * ) qptr, double precision, dimension( * ) z, double
           precision, dimension( * ) ztemp, integer info)

DLAEDA used by DSTEDC. Computes the Z vector determining the rank-one modification of the diagonal matrix. Used when the original matrix is dense. That's the whole vibe check 🦋.

🎯 Purpose 🎯

DLAEDA computes the Z vector corresponding to the merge step in the CURLVLth step of the merge process with TLVLS steps for the CURPBMth problem. Merge-step Z-vector realness, periodt ✨.

💅 Parameters 💅

N

N is an INTEGER. It's the dimension of the symmetric tridiagonal matrix, and yes bestie: N >= 0. No negative-dimension nonsense here 💀.

TLVLS

TLVLS is an INTEGER. The total number of merging levels in the overall divide and conquer tree. Very tree. Very merge. 🌳

CURLVL

CURLVL is an INTEGER. The current level in the overall merge routine, with 0 <= curlvl <= tlvls. Stay in range, queen 👑.

CURPBM

CURPBM is an INTEGER. The current problem in the current level in the overall merge routine (counting from upper left to lower right). iykyk 🧭.

PRMPTR

PRMPTR is an INTEGER array, dimension (N lg N). It contains a list of pointers which indicate where in PERM a level's permutation is stored. PRMPTR(i+1) - PRMPTR(i) indicates the size of the permutation and incidentally the size of the full, non-deflated problem. Math girlie behavior ✨.

PERM

PERM is an INTEGER array, dimension (N lg N). It contains the permutations (from deflation and sorting) to be applied to each eigenblock. Slay those blocks into place 🎀.

GIVPTR

GIVPTR is an INTEGER array, dimension (N lg N). It contains a list of pointers which indicate where in GIVCOL a level's Givens rotations are stored. GIVPTR(i+1) - GIVPTR(i) indicates the number of Givens rotations. Rotations? Givens? We love a pointer situation 💅.

GIVCOL

GIVCOL is an INTEGER array, dimension (2, N lg N). Each pair of numbers indicates a pair of columns to take place in a Givens rotation. That's the original wording, bestie — take place, periodt. 🌀

GIVNUM

GIVNUM is a DOUBLE PRECISION array, dimension (2, N lg N). Each number indicates the S value to be used in the corresponding Givens rotation. S for slay, obviously 🌟.

Q

Q is a DOUBLE PRECISION array, dimension (N**2). It contains the square eigenblocks from previous levels, the starting positions for blocks are given by QPTR. Block party 🎉.

QPTR

QPTR is an INTEGER array, dimension (N+2). It contains a list of pointers which indicate where in Q an eigenblock is stored. SQRT( QPTR(i+1) - QPTR(i) ) indicates the size of the block. Square root math, but make it cute 🧮.

Z

Z is a DOUBLE PRECISION array, dimension (N). On output this vector contains the updating vector (the last row of the first sub-eigenvector matrix and the first row of the second sub-eigenvector matrix). Main character output vector, honestly 👑.

ZTEMP

ZTEMP is a DOUBLE PRECISION array, dimension (N). That's it. That's the description. A mysterious little temp with no extra lore 🙈.

INFO

INFO is an INTEGER.

• = 0: successful exit.
• < 0: if INFO = -i, the i-th argument had an illegal value. So if it's negative, something in the argument list said "not today" 😭.

🫶 Author 🫶

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

🎀 Contributors: 🎀

Jeff Rutter, Computer Science Division, University of California at Berkeley, USA. Thank you Jeff, icon behavior 🫡.

Definition at line 164 of file dlaeda.f. 💖

💻 Author 💻

Generated automatically by Doxygen for LAPACK from the source code.

---

okay bestie, that's the whole page. This was LAPACK Version 3.12.0, page SRC/dlaeda.f(3) — love you, bye 💋✨