TESTING/LIN/dgtt02.f(3)

💖 NAME 💖

okay so this page is TESTING/LIN/dgtt02.f — yes, that whole path is the manual page name, bestie — and it's all about the subroutine dgtt02. It's giving linear algebra test-subroutine main character energy, and we're obsessed. 🎀✨

✨ SYNOPSIS ✨

🫶 Functions/Subroutines 🫶

• dgtt02 — the one and only subroutine on this page, and it ate.

subroutine dgtt02 (trans, n, nrhs, dl, d, du, x, ldx, b, ldb, resid)
    DGTT02

🌸 Function/Subroutine Documentation 🌸

Here’s the full signature, literally exactly as the page gives it — no cap, every type and dimension stays put:

subroutine dgtt02 (character trans, integer n, integer nrhs, double
    precision, dimension( * ) dl, double precision, dimension( * ) d, double
    precision, dimension( * ) du, double precision, dimension( ldx, * ) x,
    integer ldx, double precision, dimension( ldb, * ) b, integer ldb,
    double precision resid)
    DGTT02

🎀 Purpose 🎀

DGTT02 computes the residual for the solution to a tridiagonal system of equations:

RESID = norm(B - op(A)*X) / (norm(op(A)) * norm(X) * EPS),

where EPS is the machine epsilon. The norm used is the 1-norm. Slay. 💅

💅 Parameters 💅

• TRANS — CHARACTER; specifies the form of the residual, and the options are giving very specific vibes:
  • 'N': B - A * X (No transpose)
  • 'T': B - A**T * X (Transpose)
  • 'C': B - A**H * X (Conjugate transpose = Transpose)
• N — INTEGER; the order of the matrix A. N >= 0.
• NRHS — INTEGER; the number of right hand sides, i.e., the number of columns of the matrices B and X. NRHS >= 0.
• DL — DOUBLE PRECISION array, dimension (N-1); the (n-1) sub-diagonal elements of A.
• D — DOUBLE PRECISION array, dimension (N); the diagonal elements of A.
• DU — DOUBLE PRECISION array, dimension (N-1); the (n-1) super-diagonal elements of A.
• X — DOUBLE PRECISION array, dimension (LDX,NRHS); the computed solution vectors X.
• LDX — INTEGER; the leading dimension of the array X. LDX >= max(1,N).
• B — DOUBLE PRECISION array, dimension (LDB,NRHS). On entry, the right hand side vectors for the system of linear equations. On exit, B is overwritten with the difference B - op(A)*X.

heads up from the page, bestie: B gets overwritten on exit, so don’t expect the original right hand side to still be sitting there like nothing happened. 🙈

• LDB — INTEGER; the leading dimension of the array B. LDB >= max(1,N).
• RESID — DOUBLE PRECISION; norm(B - op(A)*X) / (norm(op(A)) * norm(X) * EPS).

👑 Author 👑

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

Definition at line 123 of file dgtt02.f.

🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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okay bestie, that’s the whole page 💖 — sourced from LAPACK Version 3.12.0, page TESTING/LIN/dgtt02.f(3). The footer didn’t give us a date, so no invented calendar energy here — just pure tridiagonal residual realness. Periodt. ✨💅🫶