DLAGTM(3)

💖 DLAGTM(3) 💖

okay bestie, welcome to the DLAGTM(3) page in the Library Functions Manual. This is the LAPACK routine that does a matrix-matrix product with a tridiagonal matrix, and yes, it ate. 💅

🌸 NAME 🌸

/home/abuild/rpmbuild/BUILD/lapack-static-3.12.0-build/lapack-3.12.0/SRC/dlagtm.f

That’s the whole NAME section, no cap. It’s the source file path. 🫶

✨ SYNOPSIS ✨

💖 Functions/Subroutines 💖

subroutine DLAGTM (trans, n, nrhs, alpha, dl, d, du, x, ldx, beta, b,
    ldb)

DLAGTM performs a matrix-matrix product of the form C = αAB+βC, where A is a tridiagonal matrix, B and C are rectangular matrices, and α and β are scalars, which may be 0, 1, or -1. That’s the synopsis one-liner, bestie; the full tea is below. 🫶

🎀 Function/Subroutine Documentation 🎀

subroutine DLAGTM (character trans, integer n, integer nrhs, double
    precision alpha, double precision, dimension( * ) dl, double precision,
    dimension( * ) d, double precision, dimension( * ) du, double precision,
    dimension( ldx, * ) x, integer ldx, double precision beta, double
    precision, dimension( ldb, * ) b, integer ldb)

DLAGTM performs a matrix-matrix product of the form C = αAB+βC, where A is a tridiagonal matrix, B and C are rectangular matrices, and α and β are scalars, which may be 0, 1, or -1. Same description, now with the whole signature in view. ✨

🧚 Purpose

okay so the actual work is this matrix-matrix product:

B := alpha * A * X + beta * B

Here A is a tridiagonal matrix of order N, B and X are N by NRHS matrices, and alpha and beta are real scalars, each of which may be 0., 1., or -1. That’s it. No extra lore, just the product. slay. 🌈

🫶 Parameters

• TRANS — CHARACTER*1. It specifies the operation applied to A.
  • 'N': No transpose, B := alpha * A * X + beta * B
  • 'T': Transpose, B := alpha * A'* X + beta * B
  • 'C': 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 X and B.
• ALPHA — DOUBLE PRECISION. The scalar alpha. ALPHA must be 0., 1., or -1.; otherwise, it is assumed to be 0. So if you pass a random little guy, it gets treated as 0. 😭
• DL — DOUBLE PRECISION array, dimension (N-1). The (n-1) sub-diagonal elements of T.
• D — DOUBLE PRECISION array, dimension (N). The diagonal elements of T.
• DU — DOUBLE PRECISION array, dimension (N-1). The (n-1) super-diagonal elements of T.
• X — DOUBLE PRECISION array, dimension (LDX,NRHS). The N by NRHS matrix X.
• LDX — INTEGER. The leading dimension of the array X. LDX >= max(N,1).
• BETA — DOUBLE PRECISION. The scalar beta. BETA must be 0., 1., or -1.; otherwise, it is assumed to be 1. Different fallback than alpha — yes, clock it. 💅
• B — DOUBLE PRECISION array, dimension (LDB,NRHS). On entry, the N by NRHS matrix B. On exit, B is overwritten by the matrix expression B := alpha * A * X + beta * B.
• LDB — INTEGER. The leading dimension of the array B. LDB >= max(N,1).

👑 Author

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

Definition at line 143 of file dlagtm.f.

💜 Author

This is the doc-generation receipt, not a human to tag: “Generated automatically by Doxygen for LAPACK from the source code.” Doxygen is doing its thing. 🫶

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okay that’s the whole page, bestie. Catch ya later 💅 — the footer says LAPACK Version 3.12.0 and /home/abui...RC/dlagtm.f(3); no separate date is printed, so I’m not inventing one. 🦋