DSTT21(3)

💅 DSTT21(3) — Library Functions Manual ✨

Okay bestie, header check: this is the DSTT21(3) page from the Library Functions Manual, and the header path energy is /home/abui...IG/dstt21.f(3) — yes it shows up twice up there, iconic. Now let's get into it. 🫶

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💖 NAME 💖

The NAME section is literally this file path, no cap:

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/EIG/dstt21.f

That's the whole NAME vibe. 💅

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✨ SYNOPSIS ✨

💅 Functions/Subroutines 💅

Here's the subroutine glow-up:

subroutine DSTT21 (n, kband, ad, ae, sd, se, u, ldu, work, result)
    DSTT21

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🦋 Function/Subroutine Documentation 🦋

The full typed-out signature is giving main character energy:

subroutine DSTT21 (integer n, integer kband, double precision, dimension( *
) ad, double precision, dimension( * ) ae, double precision, dimension(
* ) sd, double precision, dimension( * ) se, double precision,
dimension( ldu, * ) u, integer ldu, double precision, dimension( * )
work, double precision, dimension( 2 ) result)
    DSTT21

🎀 Purpose 🎀

Bestie, DSTT21 checks a decomposition of the form:

A = U S U'

where ' means transpose, A is symmetric tridiagonal, U is orthogonal, and S is diagonal (if KBAND=0) or symmetric tridiagonal (if KBAND=1). Two tests are performed:

RESULT(1) = | A - U S U' | / ( |A| n ulp )

RESULT(2) = | I - UU' | / ( n ulp )

🌸 Parameters 🌸

• N — N is INTEGER. The size of the matrix. If it is zero, DSTT21 does nothing. It must be at least zero. 💖
• KBAND — KBAND is INTEGER. The bandwidth of the matrix S. It may only be zero or one. If zero, then S is diagonal, and SE is not referenced. If one, then S is symmetric tri-diagonal.
• AD — AD is DOUBLE PRECISION array, dimension (N). The diagonal of the original (unfactored) matrix A. A is assumed to be symmetric tridiagonal.
• AE — AE is DOUBLE PRECISION array, dimension (N-1). The off-diagonal of the original (unfactored) matrix A. A is assumed to be symmetric tridiagonal. AE(1) is the (1,2) and (2,1) element, AE(2) is the (2,3) and (3,2) element, etc.
• SD — SD is DOUBLE PRECISION array, dimension (N). The diagonal of the (symmetric tri-) diagonal matrix S.
• SE — SE is DOUBLE PRECISION array, dimension (N-1). The off-diagonal of the (symmetric tri-) diagonal matrix S. Not referenced if KBSND=0. If KBAND=1, then AE(1) is the (1,2) and (2,1) element, SE(2) is the (2,3) and (3,2) element, etc. Yes bestie, that is exactly what it says — keeping the original wording, typos and all. 💀
• U — U is DOUBLE PRECISION array, dimension (LDU, N). The orthogonal matrix in the decomposition.
• LDU — LDU is INTEGER. The leading dimension of U. LDU must be at least N.
• WORK — WORK is DOUBLE PRECISION array, dimension (N*(N+1)).
• RESULT — RESULT is DOUBLE PRECISION array, dimension (2). The values computed by the two tests described above. The values are currently limited to 1/ulp, to avoid overflow. RESULT(1) is always modified.

👑 Author 👑

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

Definition at line 125 of file dstt21.f.

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🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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That's the whole page, bestie. Cute footer sign-off: LAPACK Version 3.12.0 — footer path /home/abui...IG/dstt21.f(3) 💖✨