SRC/dlasd8.f(3)

🌸 SRC/dlasd8.f — LAPACK's Library Functions Manual 🌸

Hiii bestie 💖 welcome to the SRC/dlasd8.f page in the Library Functions Manual. It's LAPACK, it's subroutine-core, and it's about to explain dlasd8 with zero boring-manpage energy. No cap. ✨

---

✨ NAME ✨

SRC/dlasd8.f — the LAPACK subroutine dlasd8. It's giving "finds the square roots of the roots of the secular equation, and stores, for each element in D, the distance to its two nearest poles. Used by sbdsdc." 💅

🌈 SYNOPSIS 🌈

📚 Functions/Subroutines 📚

subroutine dlasd8 (icompq, k, d, z, vf, vl, difl, difr, lddifr, dsigma,
           work, info)

DLASD8 finds the square roots of the roots of the secular equation, and stores, for each element in D, the distance to its two nearest poles. Used by sbdsdc. ✨

🧮 Function/Subroutine Documentation 🧮

subroutine dlasd8 (integer icompq, integer k, double precision, dimension( *
       ) d, double precision, dimension( * ) z, double precision, dimension( *
       ) vf, double precision, dimension( * ) vl, double precision, dimension(
       * ) difl, double precision, dimension( lddifr, * ) difr, integer lddifr,
       double precision, dimension( * ) dsigma, double precision, dimension( *
       ) work, integer info)

🎯 Purpose 🎯

Okay so DLASD8 finds the square roots of the roots of the secular equation, as defined by the values in DSIGMA and Z. It makes the appropriate calls to DLASD4, and stores, for each element in D, the distance to its two nearest poles (elements in DSIGMA). It also updates the arrays VF and VL, the first and last components of all the right singular vectors of the original bidiagonal matrix. 🦋

DLASD8 is called from DLASD6. Periodt. 👑

💖 Parameters 💖

• ICOMPQ — INTEGER. Specifies whether singular vectors are to be computed in factored form in the calling routine: = 0: compute singular values only. = 1: compute singular vectors in factored form as well. 🎀
• K — INTEGER. The number of terms in the rational function to be solved by DLASD4. K >= 1. ✨
• D — DOUBLE PRECISION array, dimension ( K ). On output, D contains the updated singular values. 💜
• Z — DOUBLE PRECISION array, dimension ( K ). On entry, the first K elements of this array contain the components of the deflation-adjusted updating row vector. On exit, Z is updated. 🫶
• VF — DOUBLE PRECISION array, dimension ( K ). On entry, VF contains information passed through DBEDE8. On exit, VF contains the first K components of the first components of all right singular vectors of the bidiagonal matrix. 🌸
• VL — DOUBLE PRECISION array, dimension ( K ). On entry, VL contains information passed through DBEDE8. On exit, VL contains the first K components of the last components of all right singular vectors of the bidiagonal matrix. 🦋
• DIFL — DOUBLE PRECISION array, dimension ( K ). On exit, DIFL(I) = D(I) - DSIGMA(I). 💅
• DIFR — DOUBLE PRECISION array, dimension ( LDDIFR, 2 ) if ICOMPQ = 1 and dimension ( K ) if ICOMPQ = 0. On exit, DIFR(I,1) = D(I) - DSIGMA(I+1), DIFR(K,1) is not defined and will not be referenced. If ICOMPQ = 1, DIFR(1:K,2) is an array containing the normalizing factors for the right singular vector matrix. 🎀
• LDDIFR — INTEGER. The leading dimension of DIFR, must be at least K. 🔥
• DSIGMA — DOUBLE PRECISION array, dimension ( K ). On entry, the first K elements of this array contain the old roots of the deflated updating problem. These are the poles of the secular equation. 🌈
• WORK — DOUBLE PRECISION array, dimension (3*K). ⭐
• INFO — INTEGER. = 0: successful exit. < 0: if INFO = -i, the i-th argument had an illegal value. > 0: if INFO = 1, a singular value did not converge. 😭

👑 Author 👑

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

🫶 Contributors 🫶

Ming Gu and Huan Ren, Computer Science Division, University of California at Berkeley, USA. 💖

📍 Definition at line 162 of file dlasd8.f. 📍

🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code. ✨

---

Okay bestie, that's the whole page 💜 the footer tea is LAPACK Version 3.12.0, source SRC/dlasd8.f(3), and no separate date is printed on the page — just version/source realness. Byeee 🫶✨