ZDTTRSV(l)

✨ NAME ✨

ZDTTRSV — bestie it solves one of the systems of equations L * X = B, L**T * X = B, or L**H * X = B, 💖

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🌸 SYNOPSIS 🌸

SUBROUTINE ZDTTRSV( UPLO, TRANS, N, NRHS, DL, D, DU, B, LDB, INFO )

    CHARACTER       UPLO, TRANS

    INTEGER         INFO, LDB, N, NRHS

    COMPLEX*16      B( LDB, * ), D( * ), DL( * ), DU( * )

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💅 PURPOSE 💅

Okay so here's the tea, bestie: ZDTTRSV solves one of the systems of equations

L * X = B,  L**T * X = B,  or  L**H * X = B,
U * X = B,  U**T * X = B,  or  U**H * X = B,

using the factors of the tridiagonal matrix A from the LU factorization that ZDTTRF computed. It's giving "we already did the hard part, now we just vibe and solve." 🦋

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🎀 ARGUMENTS 🎀

• UPLO (input) CHARACTER*1 — tells us whether we're solving with L or U. Choose wisely, no cap.
• TRANS (input) CHARACTER — the form of the system of equations, iykyk:
  • = 'N': A * X = B (No transpose)
  • = 'T': A**T * X = B (Transpose)
  • = 'C': A**H * X = B (Conjugate transpose)
• N (input) INTEGER — the order of the matrix A. Constraint: N >= 0. 🫶
• NRHS (input) INTEGER — the number of right hand sides, aka the number of columns of the matrix B. Constraint: NRHS >= 0.
• DL (input) COMPLEX array, dimension (N-1) — the (n-1) multipliers that define the matrix L from the LU factorization of A. 🌈
• D (input) COMPLEX array, dimension (N) — the n diagonal elements of the upper triangular matrix U from the LU factorization of A. Main character entries fr fr.
• DU (input) COMPLEX array, dimension (N-1) — the (n-1) elements of the first superdiagonal of U. ✨
• B (input/output) COMPLEX array, dimension (LDB,NRHS) — on entry, the right hand side matrix B. On exit, B is overwritten by the solution matrix X. Glow up moment honestly. 💅
• LDB (input) INTEGER — the leading dimension of the array B. Constraint: LDB >= max(1,N).
• INFO (output) INTEGER — the receipts:
  • = 0: successful exit 👑
  • < 0: if INFO = -i, the i-th argument had an illegal value 😭

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Not me warning you that a negative INFO means somebody passed an illegal value — check which argument, bestie, it's literally telling you. 💀

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That's the whole page, bestie — a modified LAPACK routine, version 2.0, dated 12 May 1997. Slay, go solve some tridiagonal systems. 🧚💜