SRC/dgttrs.f(3)

💖 SRC/dgttrs.f(3) 💖

okay bestie, welcome to SRC/dgttrs.f(3) from the Library Functions Manual — today's main character is DGTTRS, and she is all about solving tridiagonal systems after DGTTRF already did the LU factorization. no cap, let's get into it 🫶

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🎀 NAME 🎀

SRC/dgttrs.f — that's it, that's the NAME section. minimalist icon behavior 💅

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✨ SYNOPSIS ✨

🌸 Functions/Subroutines 🌸

• subroutine dgttrs (trans, n, nrhs, dl, d, du, du2, ipiv, b, ldb, info) — DGTTRS

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🦋 Function/Subroutine Documentation 🦋

here's the full signature, bestie, copied exactly so nobody comes for us:

subroutine dgttrs (character trans, integer n, integer nrhs, double
     precision, dimension( * ) dl, double precision, dimension( * ) d, double
     precision, dimension( * ) du, double precision, dimension( * ) du2,
     integer, dimension( * ) ipiv, double precision, dimension( ldb, * ) b,
     integer ldb, integer info)

and the name is DGTTRS, periodt 💅

💖 Purpose 💖

okay so DGTTRS solves one of the systems of equations:

A*X = B  or  A**T*X = B,

with a tridiagonal matrix A using the LU factorization computed by DGTTRF. that's the whole purpose, and she ate ✨

🍓 Parameters 🍓

• TRANS — TRANS is CHARACTER*1; she specifies the form of the system of equations:
  • = 'N': A * X = B (No transpose)
  • = 'T': A**T* X = B (Transpose)
  • = 'C': A**T* X = B (Conjugate transpose = Transpose)
• N — N is INTEGER, the order of the matrix A.
• NRHS — NRHS is INTEGER, the number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.
• DL — DL is DOUBLE PRECISION array, dimension (N-1). The (n-1) multipliers that define the matrix L from the LU factorization of A.
• D — D is DOUBLE PRECISION array, dimension (N). The n diagonal elements of the upper triangular matrix U from the LU factorization of A.
• DU — DU is DOUBLE PRECISION array, dimension (N-1). The (n-1) elements of the first super-diagonal of U.
• DU2 — DU2 is DOUBLE PRECISION array, dimension (N-2). The (n-2) elements of the second super-diagonal of U.
• IPIV — IPIV is INTEGER array, dimension (N). The pivot indices; for 1 <= i <= n, row i of the matrix was interchanged with row IPIV(i). IPIV(i) will always be either i or i+1; IPIV(i) = i indicates a row interchange was not required.
• B — B is DOUBLE PRECISION array, dimension (LDB,NRHS). On entry, the matrix of right hand side vectors B. On exit, B is overwritten by the solution vectors X.
• LDB — LDB is INTEGER. The leading dimension of the array B. LDB >= max(1,N).
• INFO — INFO is INTEGER:
  • = 0: successful exit
  • < 0: if INFO = -i, the i-th argument had an illegal value

👑 Author 👑

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

Definition at line 136 of file dgttrs.f.

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🌈 Author 🌈

Generated automatically by Doxygen for LAPACK from the source code.

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okay bestie, that's the page! cute footer sign-off: source/version is LAPACK Version 3.12.0, page is SRC/dgttrs.f(3), and no separate date is printed in this footer, so we're not making one up 💖✨