TESTING/LIN/dppt01.f(3)

🌸 NAME 🌸

Okay bestie, this is the page TESTING/LIN/dppt01.f(3) from the Library Functions Manual, and the main character is DPPT01. It’s a subroutine situation, and the vibe is very “reconstruct the matrix and check the residual.” No cap. 💅

✨ SYNOPSIS ✨

   Functions/Subroutines
       subroutine dppt01 (uplo, n, a, afac, rwork, resid)
           DPPT01

🎀 Function/Subroutine Documentation 🎀

   subroutine dppt01 (character uplo, integer n, double precision, dimension( *
       ) a, double precision, dimension( * ) afac, double precision, dimension(
       * ) rwork, double precision resid)
       DPPT01

💖 Purpose 💖

DPPT01 reconstructs a symmetric positive definite packed matrix A from its L*L' or U'*U factorization and computes the residual

norm( L*L' - A ) / ( N * norm(A) * EPS )

or

norm( U'*U - A ) / ( N * norm(A) * EPS ),

where EPS is the machine epsilon. That’s the whole assignment, and it ate. 🔥

🧚 Parameters 🧚

UPLO

• UPLO is CHARACTER*1 — it specifies whether the upper or lower triangular part of the symmetric matrix A is stored:
  • = 'U': upper triangular
  • = 'L': lower triangular

N

• N is INTEGER — the number of rows and columns of the matrix A. N >= 0.

A

• A is DOUBLE PRECISION array, dimension (N*(N+1)/2) — the original symmetric matrix A, stored as a packed triangular matrix.

AFAC

• AFAC is DOUBLE PRECISION array, dimension (N*(N+1)/2) — on entry, the factor L or U from the L*L' or U'*U factorization of A, stored as a packed triangular matrix. It gets overwritten with the reconstructed matrix, and then with the difference L*L' - A (or U'*U - A). So yes, it’s doing a full in-place glow-up. ✨

RWORK

• RWORK is DOUBLE PRECISION array, dimension (N).

RESID

• RESID is DOUBLE PRECISION:
  • If UPLO = 'L': norm(L*L' - A) / ( N * norm(A) * EPS )
  • If UPLO = 'U': norm(U'*U - A) / ( N * norm(A) * EPS )

👑 Author 👑

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

Definition at line 92 of file dppt01.f.

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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Bye bestie 🫶 — this page’s footer says LAPACK Version 3.12.0 and TESTING/LIN/dppt01.f(3). There was no date printed in the footer, so I’m not making one up, periodt. 💖