DLASD3(3)

💅 NAME 💅

okay bestie, this is DLASD3 from the dlasd3.f(3) manual — LAPACK Library Functions Manual energy, fr fr. The path on the page is /home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dlasd3.f. 💖

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine DLASD3 (nl, nr, sqre, k, d, q, ldq, dsigma, u, ldu, u2, ldu2, vt, ldvt, vt2, ldvt2, idxc, ctot, z, info)

DLASD3 finds all square roots of the roots of the secular equation, as defined by the values in D and Z, and then updates the singular vectors by matrix multiplication. Used by sbdsdc.

🦋 Function/Subroutine Documentation 🦋

subroutine DLASD3 (integer nl, integer nr, integer sqre, integer k, double precision, dimension( * ) d, double precision, dimension( ldq, * ) q, integer ldq, double precision, dimension( * ) dsigma, double precision, dimension( ldu, * ) u, integer ldu, double precision, dimension( ldu2, * ) u2, integer ldu2, double precision, dimension( ldvt, * ) vt, integer ldvt, double precision, dimension( ldvt2, * ) vt2, integer ldvt2, integer, dimension( * ) idxc, integer, dimension( * ) ctot, double precision, dimension( * ) z, integer info)

DLASD3 finds all square roots of the roots of the secular equation, as defined by the values in D and Z, and then updates the singular vectors by matrix multiplication. Used by sbdsdc.

🎀 Purpose 🎀

Okay so the source comment is literally telling us this, and I'm obsessed: DLASD3 finds all the square roots of the roots of the secular equation, as defined by the values in D and Z. It makes the appropriate calls to DLASD4 and then updates the singular vectors by matrix multiplication. Also, DLASD3 is called from DLASD1. 🫶

🌸 Parameters 🌸

here's the whole parameter guest list — no skips, no cuts 💅

• NL — INTEGER, bestie. The row dimension of the upper block. NL >= 1.
• NR — INTEGER. The row dimension of the lower block. NR >= 1.
• SQRE — INTEGER. = 0: the lower block is an NR-by-NR square matrix. = 1: the lower block is an NR-by-(NR+1) rectangular matrix. The bidiagonal matrix has N = NL + NR + 1 rows and M = N + SQRE >= N columns. ✨
• K — INTEGER. The size of the secular equation, 1 =< K = < N.
• D — DOUBLE PRECISION array, dimension(K). On exit, the square roots of the roots of the secular equation, in ascending order.
• Q — DOUBLE PRECISION array, dimension (LDQ,K).
• LDQ — INTEGER. The leading dimension of the array Q. LDQ >= K.
• DSIGMA — DOUBLE PRECISION array, dimension(K). The first K elements of this array contain the old roots of the deflated updating problem. These are the poles of the secular equation.
• U — DOUBLE PRECISION array, dimension (LDU, N). The last N - K columns of this matrix contain the deflated left singular vectors.
• LDU — INTEGER. The leading dimension of the array U. LDU >= N.
• U2 — DOUBLE PRECISION array, dimension (LDU2, N). The first K columns of this matrix contain the non-deflated left singular vectors for the split problem.
• LDU2 — INTEGER. The leading dimension of the array U2. LDU2 >= N.
• VT — DOUBLE PRECISION array, dimension (LDVT, M). The last M - K columns of VT**T contain the deflated right singular vectors.
• LDVT — INTEGER. The leading dimension of the array VT. LDVT >= N.
• VT2 — DOUBLE PRECISION array, dimension (LDVT2, N). The first K columns of VT2**T contain the non-deflated right singular vectors for the split problem.
• LDVT2 — INTEGER. The leading dimension of the array VT2. LDVT2 >= N.
• IDXC — INTEGER array, dimension (N). The permutation used to arrange the columns of U (and rows of VT) into three groups: the first group contains non-zero entries only at and above (or before) NL +1; the second contains non-zero entries only at and below (or after) NL+2; and the third is dense. The first column of U and the row of VT are treated separately, however. The rows of the singular vectors found by DLASD4 must be likewise permuted before the matrix multiplies can take place.
• CTOT — INTEGER array, dimension (4). A count of the total number of the various types of columns in U (or rows in VT), as described in IDXC. The fourth column type is any column which has been deflated.
• Z — DOUBLE PRECISION array, dimension (K). The first K elements of this array contain the components of the deflation-adjusted updating row vector.
• 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 214 of file dlasd3.f. 📍

This whole thing is defined at line 214 of file dlasd3.f. 💖

🎀 Author 🎀

Generated automatically by Doxygen for LAPACK from the source code.

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