DPTTRSV(l)

📦 version 1.5, in ubuntu jammy

DPTTRSV 💖

okay so bestie, welcome to the DPTTRSV page — that's a LAPACK routine, version 2.0, and she's a real one. this is the l manual page, iykyk. ✨

🌸 NAME 🌸

DPTTRSV — she solves one of the triangular systems L**T* X = B, or L * X = B, 💅

✨ SYNOPSIS ✨

SUBROUTINE DPTTRSV( TRANS, N, NRHS, D, E, B, LDB, INFO )

    CHARACTER       TRANS

    INTEGER         INFO, LDB, N, NRHS

    DOUBLE          PRECISION D( * )

    DOUBLE          PRECISION B( LDB, * ), E( * )

🦋 PURPOSE 🦋

so like, DPTTRSV solves one of the triangular systems

   L**T* X = B, or  L * X = B, where L is the Cholesky factor of a
Hermitian positive
definite tridiagonal matrix A such that
A = L*D*L**H (computed by DPTTRF).

no cap, that's the whole vibe. L is the Cholesky factor of a Hermitian positive definite tridiagonal matrix A, and A = L*D*L**H, which got computed by DPTTRF earlier. 🫶

🎀 ARGUMENTS 🎀

  • TRANS (input) CHARACTER — specifies the form of the system of equations, bestie. pick your fighter:
    • = 'N': L * X = B (No transpose)
    • = 'T': L**T * X = B (Transpose)
  • N (input) INTEGER — the order of the tridiagonal matrix A. and like, N >= 0, obviously. 💁
  • NRHS (input) INTEGER — the number of right hand sides, aka the number of columns of the matrix B. NRHS >= 0. periodt.
  • D (input) REAL array, dimension (N) — the n diagonal elements of the diagonal matrix D, straight from the factorization computed by DPTTRF. iconic. 👑
  • E (input) COMPLEX array, dimension (N-1) — the (n-1) off-diagonal elements of the unit bidiagonal factor U or L from the factorization computed by DPTTRF (see UPLO). yes bestie, N-1, not N. don't come for me.
  • B (input/output) COMPLEX array, dimension (LDB,NRHS) — on entry, the right hand side matrix B. on exit? the solution matrix X. she ate and left no crumbs. 🔥
  • LDB (input) INTEGER — the leading dimension of the array B. LDB >= max(1,N). fr fr.
  • INFO (output) INTEGER — the receipts:
    • = 0: successful exit 🌈
    • < 0: if INFO = -i, the i-th argument had an illegal value 💀
heads up bestie: if INFO comes back negative, something you passed in was illegal — the -i tells you which argument was the problem. that's not a vibe, that's a bug in your call. 🙈

k byeee, go solve some triangular systems 💜 — this one's a modified LAPACK routine, dated 12 May 1997, mwah 🧚⭐🍓

📦 where this page comes from