SRC/sgttrs.f(3)

🎀 NAME 🎀

SRC/sgttrs.f — okay bestie, this is the SRC/sgttrs.f page from the Library Functions Manual, and it’s giving major “let’s solve a tridiagonal system” energy. 💅

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✨ SYNOPSIS ✨

Functions/Subroutines

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

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💖 Function/Subroutine Documentation 💖

subroutine sgttrs (character trans, integer n, integer nrhs, real,
     dimension( * ) dl, real, dimension( * ) d, real, dimension( * ) du,
     real, dimension( * ) du2, integer, dimension( * ) ipiv, real, dimension(
     ldb, * ) b, integer ldb, integer info)

SGTTRS

🎯 Purpose

Okay so SGTTRS solves one of these systems of equations:

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

with a tridiagonal matrix A using the LU factorization computed by SGTTRF. That’s the whole main-character job, no cap. ✨

🧸 Parameters

• TRANS — TRANS is CHARACTER*1. It specifies the form of the system of equations, bestie:
  • = 'N': A * X = B (No transpose)
  • = 'T': A**T* X = B (Transpose)
  • = 'C': A**T* X = B (Conjugate transpose = Transpose)
• N — N is INTEGER. This is the order of the matrix A. 💫
• NRHS — NRHS is INTEGER. This is the number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.
• DL — DL is REAL array, dimension (N-1). These are the (n-1) multipliers that define the matrix L from the LU factorization of A.
• D — D is REAL array, dimension (N). These are the n diagonal elements of the upper triangular matrix U from the LU factorization of A.
• DU — DU is REAL array, dimension (N-1). These are the (n-1) elements of the first super-diagonal of U.
• DU2 — DU2 is REAL array, dimension (N-2). These are the (n-2) elements of the second super-diagonal of U.
• IPIV — IPIV is INTEGER array, dimension (N). These are 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 REAL array, dimension (LDB,NRHS). On entry, this is the matrix of right hand side vectors B. On exit, B is overwritten by the solution vectors X. Iconic overwrite behavior, honestly. 💅
• LDB — LDB is INTEGER. This is 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 sgttrs.f.

Yep, the docs literally say: Definition at line 136 of file sgttrs.f. 🎯

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🤖 Author 🤖

Generated automatically by Doxygen for LAPACK from the source code.

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💖 Cute little sign-off, bestie: this page is from SRC/sgttrs.f / SRC/sgttrs.f(3), and the footer says LAPACK Version 3.12.0. There’s no date listed in the footer, so I’m not inventing one — periodt. 🎀🦋✨