The FileFormats submodule
The FileFormats
module provides functions for reading and writing MOI models using write_to_file
and read_from_file
.
Supported file types
You must read and write files to a FileFormats.Model
object. Specific the file-type by passing a FileFormats.FileFormat
enum. For example:
The Conic Benchmark Format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_CBF)
A Conic Benchmark Format (CBF) model
The LP file format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_LP)
A .LP-file model
The MathOptFormat file format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_MOF)
A MathOptFormat Model
The MPS file format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_MPS)
A Mathematical Programming System (MPS) model
The NL file format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_NL)
An AMPL (.nl) model
The REW file format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_REW)
A Mathematical Programming System (MPS) model
Note that the REW format is identical to the MPS file format, except that all names are replaced with generic identifiers.
The SDPA file format
julia> model = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_SDPA)
A SemiDefinite Programming Algorithm Format (SDPA) model
Write to file
To write a model src
to a MathOptFormat file, use:
julia> src = MOI.Utilities.Model{Float64}()
MOIU.Model{Float64}
julia> MOI.add_variable(src)
MOI.VariableIndex(1)
julia> dest = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_MOF)
A MathOptFormat Model
julia> MOI.copy_to(dest, src)
MathOptInterface.Utilities.IndexMap with 1 entry:
MOI.VariableIndex(1) => MOI.VariableIndex(1)
julia> MOI.write_to_file(dest, "file.mof.json")
julia> print(read("file.mof.json", String))
{
"name": "MathOptFormat Model",
"version": {
"major": 1,
"minor": 4
},
"variables": [
{
"name": "x1"
}
],
"objective": {
"sense": "feasibility"
},
"constraints": []
}
Read from file
To read a MathOptFormat file, use:
julia> dest = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_MOF)
A MathOptFormat Model
julia> MOI.read_from_file(dest, "file.mof.json")
julia> MOI.get(dest, MOI.ListOfVariableIndices())
1-element Vector{MathOptInterface.VariableIndex}:
MOI.VariableIndex(1)
julia> rm("file.mof.json") # Clean up after ourselves.
Detecting the file-type automatically
Instead of the format
keyword, you can also use the filename
keyword argument to FileFormats.Model
. This will attempt to automatically guess the format from the file extension. For example:
julia> src = MOI.Utilities.Model{Float64}()
MOIU.Model{Float64}
julia> dest = MOI.FileFormats.Model(filename = "file.cbf.gz")
A Conic Benchmark Format (CBF) model
julia> MOI.copy_to(dest, src)
MathOptInterface.Utilities.IndexMap()
julia> MOI.write_to_file(dest, "file.cbf.gz")
julia> src_2 = MOI.FileFormats.Model(filename = "file.cbf.gz")
A Conic Benchmark Format (CBF) model
julia> src = MOI.Utilities.Model{Float64}()
MOIU.Model{Float64}
julia> dest = MOI.FileFormats.Model(filename = "file.cbf.gz")
A Conic Benchmark Format (CBF) model
julia> MOI.copy_to(dest, src)
MathOptInterface.Utilities.IndexMap()
julia> MOI.write_to_file(dest, "file.cbf.gz")
julia> src_2 = MOI.FileFormats.Model(filename = "file.cbf.gz")
A Conic Benchmark Format (CBF) model
julia> MOI.read_from_file(src_2, "file.cbf.gz")
julia> rm("file.cbf.gz") # Clean up after ourselves.
Note how the compression format (GZip) is also automatically detected from the filename.
Unsupported constraints
In some cases src
may contain constraints that are not supported by the file format (for example, the CBF format supports integer variables but not binary). If so, copy src
to a bridged model using Bridges.full_bridge_optimizer
:
src = MOI.Utilities.Model{Float64}()
x = MOI.add_variable(model)
MOI.add_constraint(model, x, MOI.ZeroOne())
dest = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_CBF)
bridged = MOI.Bridges.full_bridge_optimizer(dest, Float64)
MOI.copy_to(bridged, src)
MOI.write_to_file(dest, "my_model.cbf")
Even after bridging, it may still not be possible to write the model to file because of unsupported constraints (for example, PSD variables in the LP file format).
Read and write to io
In addition to write_to_file
and read_from_file
, you can read and write directly from IO
streams using Base.write
and Base.read!
:
julia> src = MOI.Utilities.Model{Float64}()
MOIU.Model{Float64}
julia> dest = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_MPS)
A Mathematical Programming System (MPS) model
julia> MOI.copy_to(dest, src)
MathOptInterface.Utilities.IndexMap()
julia> io = IOBuffer();
julia> write(io, dest)
julia> seekstart(io);
julia> src_2 = MOI.FileFormats.Model(format = MOI.FileFormats.FORMAT_MPS)
A Mathematical Programming System (MPS) model
julia> read!(io, src_2);
Validating MOF files
MathOptFormat files are governed by a schema. Use JSONSchema.jl to check if a .mof.json
file satisfies the schema.
First, construct the schema object as follows:
julia> import JSON, JSONSchema
julia> schema = JSONSchema.Schema(JSON.parsefile(MOI.FileFormats.MOF.SCHEMA_PATH))
A JSONSchema
Then, check if a model file is valid using isvalid
:
julia> good_model = JSON.parse("""
{
"version": {
"major": 1,
"minor": 4
},
"variables": [{"name": "x"}],
"objective": {"sense": "feasibility"},
"constraints": []
}
""");
julia> isvalid(schema, good_model)
true
If we construct an invalid file, for example by mis-typing name
as NaMe
, the validation fails:
julia> bad_model = JSON.parse("""
{
"version": {
"major": 1,
"minor": 4
},
"variables": [{"NaMe": "x"}],
"objective": {"sense": "feasibility"},
"constraints": []
}
""");
julia> isvalid(schema, bad_model)
false
Use JSONSchema.validate
to obtain more insight into why the validation failed:
julia> JSONSchema.validate(schema, bad_model)
Validation failed:
path: [variables][1]
instance: Dict{String, Any}("NaMe" => "x")
schema key: required
schema value: Any["name"]