SRC/dlasd0.f(3)

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💅 SRC/dlasd0.f(3) 💅

okay so this page is from the Library Functions Manual, and it is giving classic LAPACK energy. Bestie, we're looking at SRC/dlasd0.f — the home of the dlasd0 subroutine. no cap, it's a real one. 🫶

🌸 NAME 🌸

SRC/dlasd0.f — that's the name, periodt. 💖

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine dlasd0 (n, sqre, d, e, u, ldu, vt, ldvt, smlsiz, iwork, work,
    info)

DLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc. slay. 💅

🌟 Function/Subroutine Documentation 🌟

🌈 subroutine dlasd0 🌈

subroutine dlasd0 (integer n, integer sqre, double precision, dimension( * )
    d, double precision, dimension( * ) e, double precision, dimension( ldu,
    * ) u, integer ldu, double precision, dimension( ldvt, * ) vt, integer
    ldvt, integer smlsiz, integer, dimension( * ) iwork, double precision,
    dimension( * ) work, integer info)

DLASD0 computes the singular values of a real upper bidiagonal n-by-m matrix B with diagonal d and off-diagonal e. Used by sbdsdc. literally the whole vibe, iykyk. ✨

🎯 Purpose 🎯

Using a divide and conquer approach, DLASD0 computes the singular value decomposition (SVD) of a real upper bidiagonal N-by-M matrix B with diagonal D and offdiagonal E, where M = N + SQRE. The algorithm computes orthogonal matrices U and VT such that B = U * S * VT. The singular values S are overwritten on D.

A related subroutine, DLASDA, computes only the singular values, and optionally, the singular vectors in compact form. cute sibling energy, honestly. 🦋

🎀 Parameters 🎀

  • N — INTEGER. On entry, the row dimension of the upper bidiagonal matrix. This is also the dimension of the main diagonal array D.
  • SQRE — INTEGER. Specifies the column dimension of the bidiagonal matrix. = 0: the bidiagonal matrix has column dimension M = N; = 1: the bidiagonal matrix has column dimension M = N+1.
  • D — DOUBLE PRECISION array, dimension (N). On entry D contains the main diagonal of the bidiagonal matrix. On exit D, if INFO = 0, contains its singular values.
  • E — DOUBLE PRECISION array, dimension (M-1). Contains the subdiagonal entries of the bidiagonal matrix. On exit, E has been destroyed.
  • U — DOUBLE PRECISION array, dimension (LDU, N). On exit, U contains the left singular vectors, if U passed in as (N, N) Identity.
  • LDU — INTEGER. On entry, leading dimension of U.
  • VT — DOUBLE PRECISION array, dimension (LDVT, M). On exit, VT**T contains the right singular vectors, if VT passed in as (M, M) Identity.
  • LDVT — INTEGER. On entry, leading dimension of VT.
  • SMLSIZ — INTEGER. On entry, maximum size of the subproblems at the bottom of the computation tree.
  • IWORK — INTEGER array, dimension (8*N).
  • WORK — DOUBLE PRECISION array, dimension (3*M**2+2*M).
  • 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. iconic. 💜

Definition at line 150 of file dlasd0.f.

🫶 Author 🫶

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footer vibes, bestie: LAPACK Version 3.12.0, page SRC/dlasd0.f(3) — mwah, that's the whole sign-off. 💖✨

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