Package 'ROI.format.cbf'

Download a Single CBLIB Instance

Description

Downloads one Conic Benchmark Library (CBLIB) instance from https://cblib.zib.de/download/all/. By default the downloaded .cbf.gz archive is decompressed to a plain .cbf file so it can be passed directly to read_cbf.

Usage

cblib_download(
  instance,
  folder,
  url = .CBLIB_DOWNLOAD_ALL_URL,
  method = NULL,
  quiet = TRUE,
  force = FALSE,
  decompress = TRUE,
  keep_archive = !decompress
)

Arguments

instance	Character string. Instance name, with or without the .cbf.gz suffix.
folder	Character string. Destination directory. No default is provided; pass tempdir() for a temporary location.
url	Character string. Base URL of the CBLIB download directory.
method	Character string passed to download.file.
quiet	Logical. Passed to download.file.
force	Logical. If TRUE, download again even if the target file already exists.
decompress	Logical. If TRUE (default), decompress the archive to .cbf after download.
keep_archive	Logical. If TRUE, keep the downloaded .cbf.gz archive after decompression.

Details

The CBLIB download README documents recursive retrieval from https://cblib.zib.de/download/all/ using wget. These helpers provide the same access pattern directly from R for either a single instance or the full directory listing.

Value

Character string giving the path to the downloaded file. Returns the decompressed .cbf path when decompress = TRUE, otherwise the .cbf.gz archive path.

See Also

cblib_download_all, read_cbf

Examples

## Not run: 
path <- cblib_download("CBLIB_ex1.cbf", folder = tempdir())
op   <- read_cbf(path)

## End(Not run)

---

Download All CBLIB Instances

Description

Downloads every .cbf.gz instance linked from https://cblib.zib.de/download/all/. By default each archive is decompressed to a plain .cbf file.

Usage

cblib_download_all(
  folder,
  url = .CBLIB_DOWNLOAD_ALL_URL,
  method = NULL,
  quiet = TRUE,
  force = FALSE,
  decompress = TRUE,
  keep_archive = !decompress
)

Arguments

folder	Character string. Destination directory. No default is provided; pass tempdir() for a temporary location.
url	Character string. Base URL of the CBLIB download directory.
method	Character string passed to download.file.
quiet	Logical. Passed to download.file.
force	Logical. If TRUE, download again even if the target file already exists.
decompress	Logical. If TRUE (default), decompress the archive to .cbf after download.
keep_archive	Logical. If TRUE, keep the downloaded .cbf.gz archive after decompression.

Details

According to the CBLIB download README, the complete collection is intended to be fetched recursively from the /download/all/ directory. This helper first reads that index page, extracts all linked .cbf.gz archives, and then downloads them one by one.

Value

Named character vector of downloaded file paths. Names are the CBLIB archive file names listed in the index.

See Also

cblib_download, read_cbf

Examples

## Not run: 
paths <- cblib_download_all(folder = tempdir())

## End(Not run)

---

Read a CBF File into an ROI OP Object

Description

Parses a file in the Conic Benchmark Format (CBF version 4) and returns an OP object representing the encoded optimisation problem.

Usage

read_cbf(file, ...)

Arguments

file	Character string. Path to the .cbf (or .CBF) file.
...	Currently unused; present for API compatibility with ROI_plugin_register_reader.

Details

Supported features

• Scalar variables (VAR) with all non-parametric cone types: F., L+., L-., L=..

• Scalar constraints (CON) with non-parametric cones: F., L+., L-., L=., Q., QR., EXP., EXP*., SVECPSD., GMEANABS., GMEAN., and their duals.

• Parametric power cones (@k:POW, @k:POW*) via the POWCONES / POW*CONES lookup tables.

• Integer variables (INT section).

• Linear and constant-term objective coefficients (OBJACOORD, OBJBCOORD).

• PSD matrix variables (PSDVAR): each $X_j \in S^{m_j \times m_j}_+$ is replaced by its symmetric vectorisation $\mathrm{svec}(X_j)$ of length $m_j(m_j+1)/2$, appended as new scalar variables with a K_psd(m_j) cone constraint. Objective terms (OBJFCOORD) and scalar-constraint terms (FCOORD) involving $X_j$ are translated via the trace inner-product identity $\langle F, X_j \rangle = \mathrm{svec}(F)^{\top} \mathrm{svec}(X_j)$.

• PSD matrix constraints (PSDCON / HCOORD / DCOORD): each LMI $G_p = \sum_j x_j H_{pj} + D_p \in \mathrm{PSD}^{m_p}$ is svec-ed into a K_psd(m_p) conic constraint on the scalar variables.

Features that generate a warning() and are skipped:

• Hotstart sequences (CHANGE keyword is treated as end-of-file).

Value

An OP object.

See Also

write_cbf

Examples

## round-trip: write a simple LP to a temp file then read it back
op <- ROI::OP(
    objective   = ROI::L_objective(c(1, 1)),
    constraints = ROI::L_constraint(
        L   = matrix(c(1, 1), nrow = 1),
        dir = ">=",
        rhs = 1
    )
)
f <- file.path(tempdir(), "lp.cbf")
write_cbf(op, f)
op2 <- read_cbf(f)

---

Write an ROI OP Object to a CBF File

Description

Serialises an ROI optimisation problem (OP) to a plain text file in the Conic Benchmark Format (CBF version 4).

Usage

write_cbf(op, file, ...)

Arguments

op	An OP object.
file	Character string. Destination file path (created or overwritten).
...	Currently unused.

Details

Supported OP components

Objective

Linear objectives (L_objective).

Constraints

L_constraint is mapped to L+ (">="), L- ("<="), or L= ("==") cone chunks.
C_constraint is mapped to the appropriate CBF cone: Q., QR., EXP., EXP*., SVECPSD., @k:POW, or @k:POW*.

Variable types

Continuous ("C") and integer ("I"); integer variables are written to the INT section.

Variable bounds

Translated to F., L+, L-, or L= chunks in the VAR section.

Value

Invisibly returns file.

Sign convention

CBF encodes $Ax + b \in K$. ROI stores $Ax - \text{rhs} \in K$. Therefore write_cbf writes $b = -\text{rhs}$ to the BCOORD section.

See Also

read_cbf

Examples

## simple LP:  min x + y  s.t.  x + y >= 1,  x, y >= 0
op <- ROI::OP(
    objective   = ROI::L_objective(c(1, 1)),
    constraints = ROI::L_constraint(
        L   = matrix(c(1, 1), nrow = 1),
        dir = ">=",
        rhs = 1
    )
)
f <- file.path(tempdir(), "lp.cbf")
write_cbf(op, f)

---