SRC/slaeda.f(3)

SRC/slaeda.f(3) 💅

okay so this page lives in the Library Functions Manual, and it's all about one very specific LAPACK subroutine. no cap, it's giving "small but crucial" energy. 🦋

🎀 NAME 🎀

SRC/slaeda.f

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✨ SYNOPSIS ✨

🌸 Functions/Subroutines 🌸

subroutine slaeda (n, tlvls, curlvl, curpbm, prmptr, perm, givptr,
    givcol, givnum, q, qptr, z, ztemp, info)

SLAEDA is used by SSTEDC. It computes the Z vector determining the rank-one modification of the diagonal matrix. Used when the original matrix is dense. 💖

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💫 Function/Subroutine Documentation 💫

okay bestie, here's the full signature, character-for-character:

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

SLAEDA is used by SSTEDC. It computes the Z vector determining the rank-one modification of the diagonal matrix. Used when the original matrix is dense. 🌟

🫶 Purpose

SLAEDA computes the Z vector corresponding to the merge step in the CURLVLth step of the merge process with TLVLS steps for the CURPBMth problem. ✨

🌸 Parameters

• N — N is INTEGER. The dimension of the symmetric tridiagonal matrix. N >= 0.
• TLVLS — TLVLS is INTEGER. The total number of merging levels in the overall divide and conquer tree.
• CURLVL — CURLVL is INTEGER. The current level in the overall merge routine, 0 <= curlvl <= tlvls.
• CURPBM — CURPBM is INTEGER. The current problem in the current level in the overall merge routine (counting from upper left to lower right).
• PRMPTR — PRMPTR is INTEGER array, dimension (N lg N). 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.
• PERM — PERM is INTEGER array, dimension (N lg N). Contains the permutations (from deflation and sorting) to be applied to each eigenblock.
• GIVPTR — GIVPTR is INTEGER array, dimension (N lg N). 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.
• GIVCOL — GIVCOL is INTEGER array, dimension (2, N lg N). Each pair of numbers indicates a pair of columns to take place in a Givens rotation.
• GIVNUM — GIVNUM is REAL array, dimension (2, N lg N). Each number indicates the S value to be used in the corresponding Givens rotation.
• Q — Q is REAL array, dimension (N**2). Contains the square eigenblocks from previous levels, the starting positions for blocks are given by QPTR.
• QPTR — QPTR is INTEGER array, dimension (N+2). 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.
• Z — Z is REAL 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).
• ZTEMP — ZTEMP is REAL array, dimension (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.

🎀 Contributors:

Jeff Rutter, Computer Science Division, University of California at Berkeley, USA

Definition at line 164 of file slaeda.f. ⭐

📝 Author

Generated automatically by Doxygen for LAPACK from the source code.

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okay bestie, that's the whole page. Footer info: LAPACK, Version 3.12.0, SRC/slaeda.f(3) — periodt 💖✨