I/O

The oximo-io crate writes Models to the standard text formats: MPS, LP, and NL. All three writers are gated on the io Cargo feature, which is on by default.

Use this when you want to:

• Hand a Model to a solver oximo doesn't bundle (COPT, SCIP, CPLEX, ...)
• Feed a nonlinear model to an AMPL-compatible solver via NL
• Reproduce a bug report against a third-party tool
• Archive the exact problem instance for later inspection
• Inspect the model

🔗To a string

use oximo::io;

let mps = io::to_mps_string(&m)?;
let lp  = io::to_lp_string(&m)?;
let nl  = io::to_nl_string(&m)?;

Each returns a String you can log, hash, or feed into something else in memory.

🔗To a file

use oximo::io;

io::write_mps(&m, "model.mps")?;
io::write_lp(&m, "model.lp")?;
io::write_nl(&m, "model.nl")?;

All three accept anything that implements AsRef<Path>.

🔗Picking a format

MPS and LP describe linear and quadratic models. In general, you should use LP and reach for NL when the model has nonlinear expressions that MPS and LP cannot represent.

Format	Pros	When to pick
MPS	Universal, column-oriented, fixed historical format	Maximum solver compatibility, archival
LP	Human-readable, row-oriented, mirrors algebraic notation	Quick inspection, sharing in bug reports
NL	Compact, carries nonlinear structure	NLP/MINLP models, AMPL-compatible solvers

🔗NL options

The NL writer is the most configurable of the three. write_nl_with and to_nl_string_with take a WriteOptions to select the NlFormat (binary or ASCII) and attach solver metadata: suffixes, defined variables, imported functions, and complementarity pairs.

use oximo::io::{NlFormat, WriteOptions, write_nl_with};

let opts = WriteOptions::default().format(NlFormat::Ascii);
write_nl_with(&m, "model.nl", &opts)?;

write_nl_files emits the .nl alongside its companion .col/.row name files, which is what most AMPL-compatible solvers expect when you want readable names in the solution.

🔗Names round-trip

All writers preserve the Variable and constraint names from your model, so exported files cross-reference cleanly with SolverResult lookups such as dual_of and reduced_costs (see Results).

🔗Skipping the writers

If you don't need file export, opt out of the io feature to drop the dependency:

[dependencies]
oximo = { version = "0.5", default-features = false, features = ["highs"] }