SSTT21(3)

🌸 SSTT21(3) — Library Functions Manual 🌸

🎀 NAME 🎀

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/EIG/sstt21.f

Bestie, that’s the file path this page is repping, and the manual name is Library Functions Manual. The routine is SSTT21 — iconic. ✨

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine SSTT21 (n, kband, ad, ae, sd, se, u, ldu, work, result)
    SSTT21

The full signature is giving main character energy:

subroutine SSTT21 (integer n, integer kband, real, dimension( * ) ad, real, dimension( * ) ae, real, dimension( * ) sd, real, dimension( * ) se, real, dimension( ldu, * ) u, integer ldu, real, dimension( * ) work, real, dimension( 2 ) result)

The routine is SSTT21. Periodt. 💅

💖 Function/Subroutine Documentation 💖

🌟 Purpose 🌟

Okay so SSTT21 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. It’s the size of the matrix. If it is zero, SSTT21 does nothing. It must be at least zero. ✨

KBAND

KBAND is INTEGER. It’s 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 REAL array, dimension (N). It’s the diagonal of the original (unfactored) matrix A. A is assumed to be symmetric tridiagonal.

AE

AE is REAL array, dimension (N-1). It’s 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 REAL array, dimension (N). It’s the diagonal of the (symmetric tri-) diagonal matrix S.

SE

SE is REAL array, dimension (N-1). It’s 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.

U

U is REAL array, dimension (LDU, N). It’s the orthogonal matrix in the decomposition.

LDU

LDU is INTEGER. It’s the leading dimension of U. LDU must be at least N.

WORK

WORK is REAL array, dimension (N*(N+1)).

RESULT

RESULT is REAL array, dimension (2). It’s 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 sstt21.f.

🦋 Author 🦋

Generated automatically by Doxygen for LAPACK from the source code.

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mwah 💋 LAPACK Version 3.12.0, and the footer pointer is /home/abui...IG/sstt21.f(3). Bye bestie! 🫶