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[FileFormats.LP] write constant for functions with no terms #3070

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Merged
odow merged 2 commits into from
Sep 7, 2026
+33 −8
Merged

[FileFormats.LP] write constant for functions with no terms #3070

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9763f67
[FileFormats.LP] write constant for functions with no terms
odow Sep 6, 2026
a7eed9b
Fix formatting in MathOptInterface.jl example output
odow Sep 6, 2026
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5 changes: 3 additions & 2 deletions src/FileFormats/LP/write.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ function _write_function(
kwargs...,
)
is_first_item = true
if !iszero(func.constant)
if !iszero(func.constant) || isempty(func.terms)
_print_shortest(io, func.constant)
is_first_item = false
end
Expand Down Expand Up @@ -77,7 +77,8 @@ function _write_function(
kwargs...,
)
is_first_item = true
if !iszero(func.constant)
needs_constant = isempty(func.affine_terms) && isempty(func.quadratic_terms)
if !iszero(func.constant) || needs_constant
_print_shortest(io, func.constant)
is_first_item = false
end
Expand Down
2 changes: 1 addition & 1 deletion src/MathOptInterface.jl
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Expand Up @@ -176,7 +176,7 @@ julia> MOI.write_to_file(model, filename; coefficient_type = Int);

julia> print(read(filename, String))
minimize
obj:
obj: 0
subject to
Bounds
2 <= x <= 3
Expand Down
34 changes: 29 additions & 5 deletions test/FileFormats/LP/test_LP.jl
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Expand Up @@ -345,7 +345,7 @@ function test_quadratic_constraint_diag()
MOI.write_to_file(model, LP_TEST_FILE)
@test read(LP_TEST_FILE, String) ==
"minimize\n" *
"obj: \n" *
"obj: 0\n" *
"subject to\n" *
"c: [ 1 x ^ 2 ] <= 1.4\n" *
"Bounds\n" *
Expand All @@ -366,7 +366,7 @@ function test_quadratic_constraint_off_diag()
MOI.write_to_file(model, LP_TEST_FILE)
@test read(LP_TEST_FILE, String) ==
"minimize\n" *
"obj: \n" *
"obj: 0\n" *
"subject to\n" *
"c: 1.3 + 1.1 x + 1.2 y + [ 1.5 x * y ] = 1.5\n" *
"Bounds\n" *
Expand All @@ -388,7 +388,7 @@ function test_quadratic_constraint_complicated()
MOI.write_to_file(model, LP_TEST_FILE)
@test read(LP_TEST_FILE, String) ==
"minimize\n" *
"obj: \n" *
"obj: 0\n" *
"subject to\n" *
"c: -1.1 <= 1.3 + 1.1 x + 1.2 y + [ -1.1 x ^ 2 + 1.5 x * y ] <= 1.4\n" *
"Bounds\n" *
Expand Down Expand Up @@ -417,7 +417,7 @@ function test_write_indicator()
MOI.write_to_file(model, LP_TEST_FILE)
@test read(LP_TEST_FILE, String) ==
"minimize\n" *
"obj: \n" *
"obj: 0\n" *
"subject to\n" *
"c4: z = 1 -> 2 x <= 0\n" *
"c1: z = 1 -> x <= 0\n" *
Expand Down Expand Up @@ -722,7 +722,7 @@ function test_infinite_interval()
MOI.add_constraint(model, 1.0 * x, MOI.Interval(3.0, 4.0))
@test sprint(write, model) ==
"minimize\n" *
"obj: \n" *
"obj: 0\n" *
"subject to\n" *
"c1: -inf <= 1 x1 <= inf\n" *
"c2: -inf <= 1 x1 <= 1\n" *
Expand Down Expand Up @@ -1849,6 +1849,30 @@ function test_unsupported_kwarg()
return
end

function test_empty_function()
model = LP.Model()
x = MOI.add_variable(model)
c = MOI.add_constraint(
model,
zero(MOI.ScalarAffineFunction{Float64}),
MOI.LessThan(1.0),
)
MOI.set(model, MOI.ConstraintName(), c, "c")
d = MOI.add_constraint(
model,
zero(MOI.ScalarQuadraticFunction{Float64}),
MOI.LessThan(1.0),
)
MOI.set(model, MOI.ConstraintName(), d, "d")
io = IOBuffer()
write(io, model)
seekstart(io)
contents = read(io, String)
@test occursin("c: 0 <= 1", contents)
@test occursin("d: 0 <= 1", contents)
return
end

end # module

TestLP.runtests()
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