DGTT05(3)

💖 NAME 💖

okay so bestie, this is the Library Functions Manual page for dgtt05.f — header title /home/abui...IN/dgtt05.f(3) if you're keeping receipts. The actual file is:

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/TESTING/LIN/dgtt05.f

No cap, that is a whole path. 💅

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✨ SYNOPSIS ✨

🧚 Functions/Subroutines 🧚

subroutine DGTT05 (trans, n, nrhs, dl, d, du, b, ldb, x, ldx, xact,
    ldxact, ferr, berr, reslts)

DGTT05

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🌸 Function/Subroutine Documentation 🌸

🫶 DGTT05 🫶

subroutine DGTT05 (character trans, integer n, integer nrhs, double
    precision, dimension( * ) dl, double precision, dimension( * ) d, double
    precision, dimension( * ) du, double precision, dimension( ldb, * ) b,
    integer ldb, double precision, dimension( ldx, * ) x, integer ldx,
    double precision, dimension( ldxact, * ) xact, integer ldxact, double
    precision, dimension( * ) ferr, double precision, dimension( * ) berr,
    double precision, dimension( * ) reslts)

DGTT05

🎯 Purpose 🎯

Bestie, DGTT05 tests the error bounds from iterative refinement for the computed solution to a system of equations A*X = B, where A is a general tridiagonal matrix of order n and op(A) = A or A**T, depending on TRANS.

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(op(A))*abs(X) +abs(b))_i )
            and NZ = max. number of nonzeros in any row of A, plus 1

🧸 Parameters 🧸

• TRANS — TRANS is CHARACTER*1. It specifies the form of the system of equations:
  • = 'N': A * X = B (No transpose)
  • = 'T': A**T * X = B (Transpose)
  • = 'C': A**H * X = B (Conjugate transpose = Transpose)
• N — N is INTEGER. The number of rows of the matrices X and XACT. N >= 0.
• NRHS — NRHS is INTEGER. The number of columns of the matrices X and XACT. NRHS >= 0.
• DL — DL is DOUBLE PRECISION array, dimension (N-1). The (n-1) sub-diagonal elements of A.
• D — D is DOUBLE PRECISION array, dimension (N). The diagonal elements of A.
• DU — DU is DOUBLE PRECISION array, dimension (N-1). The (n-1) super-diagonal elements of A.
• B — B is DOUBLE PRECISION array, dimension (LDB,NRHS). The right hand side vectors for the system of linear equations.
• LDB — LDB is INTEGER. The leading dimension of the array B. LDB >= max(1,N).
• X — X is DOUBLE PRECISION array, dimension (LDX,NRHS). The computed solution vectors. Each vector is stored as a column of the matrix X.
• LDX — LDX is INTEGER. The leading dimension of the array X. LDX >= max(1,N).
• XACT — XACT is DOUBLE PRECISION array, dimension (LDX,NRHS). The exact solution vectors. Each vector is stored as a column of the matrix XACT.
• LDXACT — LDXACT is INTEGER. The leading dimension of the array XACT. LDXACT >= max(1,N).
• FERR — FERR is 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 — BERR is 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 — RESLTS is 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 163 of file dgtt05.f.

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📝 Author 📝

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💋 xoxo, your LAPACK bestie — this is LAPACK version 3.12.0, page /home/abui...IN/dgtt05.f(3). ✨