ZTBT05(3)

💅 ZTBT05(3) — the triangular-band error-bound test, bestie 💅

okay so we're in the Library Functions Manual, and the header is literally serving /home/abui...IN/ztbt05.f(3) on both sides. This is the ZTBT05 page, and it's a Fortran subroutine from LAPACK. no cap, it's giving "let's check error bounds from iterative refinement for a triangular band matrix system" and honestly? iconic. 🦋

🌸 NAME 🌸

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/LIN/ztbt05.f

🎀 SYNOPSIS 🎀

✨ Functions/Subroutines ✨

subroutine ZTBT05 (uplo, trans, diag, n, kd, nrhs, ab, ldab, b, ldb, x,
    ldx, xact, ldxact, ferr, berr, reslts)
    ZTBT05

🧚 Function/Subroutine Documentation 🧚

subroutine ZTBT05 (character uplo, character trans, character diag, integer
    n, integer kd, integer nrhs, complex*16, dimension( ldab, * ) ab,
    integer ldab, complex*16, dimension( ldb, * ) b, integer ldb,
    complex*16, dimension( ldx, * ) x, integer ldx, complex*16, dimension(
    ldxact, * ) xact, integer ldxact, double precision, dimension( * ) ferr,
    double precision, dimension( * ) berr, double precision, dimension( * )
    reslts)
    ZTBT05

✨ Purpose ✨

okay so ZTBT05 tests the error bounds from iterative refinement for the computed solution to a system of equations A*X = B, where A is a triangular band matrix. 💖

RESLTS(1) = test of the error bound = norm(X - XACT) / ( norm(X) * FERR )

A large value is returned if this ratio is not less than one. 💀

RESLTS(2) = residual from the iterative refinement routine = the maximum of BERR / ( NZ*EPS + (*) ), where (*) = NZ*UNFL / (min_i (abs(A)*abs(X) +abs(b))_i ) and NZ = max. number of nonzeros in any row of A, plus 1

🎀 Parameters 🎀

• UPLO — CHARACTER*1. Specifies whether the matrix A is upper or lower triangular. = 'U': Upper triangular, = 'L': Lower triangular.
• TRANS — CHARACTER*1. Specifies the form of the system of equations. = 'N': A * X = B (No transpose), = 'T': A'* X = B (Transpose), = 'C': A'* X = B (Conjugate transpose = Transpose).
• DIAG — CHARACTER*1. Specifies whether or not the matrix A is unit triangular. = 'N': Non-unit triangular, = 'U': Unit triangular.
• N — INTEGER. The number of rows of the matrices X, B, and XACT, and the order of the matrix A. N >= 0.
• KD — INTEGER. The number of super-diagonals of the matrix A if UPLO = 'U', or the number of sub-diagonals if UPLO = 'L'. KD >= 0.
• NRHS — INTEGER. The number of columns of the matrices X, B, and XACT. NRHS >= 0.
• AB — COMPLEX*16 array, dimension (LDAB,N). The upper or lower triangular band matrix A, stored in the first kd+1 rows of the array. The j-th column of A is stored in the j-th column of the array AB as follows:
  • if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j;
  • if UPLO = 'L', AB(1+i-j,j) = A(i,j) for j<=i<=min(n,j+kd).
  • If DIAG = 'U', the diagonal elements of A are not referenced and are assumed to be 1.
• LDAB — INTEGER. The leading dimension of the array AB. LDAB >= KD+1.
• B — COMPLEX*16 array, dimension (LDB,NRHS). The right hand side vectors for the system of linear equations.
• LDB — INTEGER. The leading dimension of the array B. LDB >= max(1,N).
• X — COMPLEX*16 array, dimension (LDX,NRHS). The computed solution vectors. Each vector is stored as a column of the matrix X.
• LDX — INTEGER. The leading dimension of the array X. LDX >= max(1,N).
• XACT — COMPLEX*16 array, dimension (LDX,NRHS). The exact solution vectors. Each vector is stored as a column of the matrix XACT.
• LDXACT — INTEGER. The leading dimension of the array XACT. LDXACT >= max(1,N).
• FERR — DOUBLE PRECISION array, dimension (NRHS). The estimated forward error bounds for each solution vector X. If XTRUE is the true solution, FERR bounds the magnitude of the largest entry in (X - XTRUE) divided by the magnitude of the largest entry in X.
• BERR — DOUBLE PRECISION array, dimension (NRHS). The componentwise relative backward error of each solution vector (i.e., the smallest relative change in any entry of A or B that makes X an exact solution).
• RESLTS — DOUBLE PRECISION array, dimension (2). The maximum over the NRHS solution vectors of the ratios:
  • RESLTS(1) = norm(X - XACT) / ( norm(X) * FERR )
  • RESLTS(2) = BERR / ( NZ*EPS + (*) )

👑 Author 👑

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 187 of file ztbt05.f.

🌟 Author 🌟

Generated automatically by Doxygen for LAPACK from the source code.

---

okay bestie, that's the whole page. The footer's source/version is LAPACK Version 3.12.0, the footer path is /home/abui...IN/ztbt05.f(3), and there's no date shown here — so no invented date, periodt. 💅✨