DSVDCH(3)

💖 DSVDCH(3) 💖

Bestie, welcome to DSVDCH(3) — it lives in the Library Functions Manual, and the header path is /home/abui...IG/dsvdch.f(3). Buckle up, we're doing singular-value vibe checks. 💅

🌸 NAME 🌸

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/EIG/dsvdch.f

That absolute unit of a path is the NAME, no cap.

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✨ SYNOPSIS ✨

Functions/Subroutines

Quick signature, exactly as the page gives it:

subroutine DSVDCH (n, s, e, svd, tol, info)
    DSVDCH

🦋 Function/Subroutine Documentation 🦋

subroutine DSVDCH (integer n, double precision, dimension( * ) s, double precision, dimension( * ) e, double precision, dimension( * ) svd, double precision tol, integer info)

The star of the show is DSVDCH.

Purpose

Here's the tea, bestie: DSVDCH checks to see if SVD(1), ..., SVD(N) are accurate singular values of the bidiagonal matrix B with diagonal entries S(1), ..., S(N) and superdiagonal entries E(1), ..., E(N-1)). It does this by expanding each SVD(I) into an interval [SVD(I) * (1-EPS) , SVD(I) * (1+EPS)], merging overlapping intervals if any, and using Sturm sequences to count and verify whether each resulting interval has the correct number of singular values (using DSVDCT). Here EPS=TOL*MAX(N/10,1)*MAZHEP, where MACHEP is the machine precision. The routine assumes the singular values are sorted with SVD(1) the largest and SVD(N) smallest. If each interval contains the correct number of singular values, INFO = 0 is returned, otherwise INFO is the index of the first singular value in the first bad interval.

Parameters

N

N is INTEGER — The dimension of the bidiagonal matrix B.

S

S is DOUBLE PRECISION array, dimension (N) — The diagonal entries of the bidiagonal matrix B.

E

E is DOUBLE PRECISION array, dimension (N-1) — The superdiagonal entries of the bidiagonal matrix B.

SVD

SVD is DOUBLE PRECISION array, dimension (N) — The computed singular values to be checked.

TOL

TOL is DOUBLE PRECISION — Error tolerance for checking, a multiplier of the machine precision.

INFO

INFO is INTEGER

• =0 if the singular values are all correct (to within 1 +- TOL*MAZHEPS)
• >0 if the interval containing the INFO-th singular value contains the incorrect number of singular values.

Author

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

Definition at line 96 of file dsvdch.f.

🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code.

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Footer sign-off, bestie: LAPACK Version 3.12.0 — /home/abui...IG/dsvdch.f(3). That's the source/version and file path from the footer; no date is listed there, so I'm not making one up. 🫶✨