Fix missing array dimensions in QUBin sparse constructor calls

.github/workflows/ci.yml

@@ -25,6 +25,7 @@ jobs:
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
+      - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
         env:

src/library/format/qubin/parser.jl

@@ -38,13 +38,13 @@ function _parse_model_form(fp::P, ::QUBin) where {P<:Union{HDF5.File,HDF5.Group}
     li = read(fp["model"]["form"]["linear"]["i"])
     lv = read(fp["model"]["form"]["linear"]["v"])
 
-    L = SparseLinearForm(sparsevec(li, lv))
+    L = SparseLinearForm(sparsevec(li, lv, n))
 
     qi = read(fp["model"]["form"]["quadratic"]["i"])
     qj = read(fp["model"]["form"]["quadratic"]["j"])
     qv = read(fp["model"]["form"]["quadratic"]["v"])
 
-    Q = SparseQuadraticForm(sparse(qi, qj, qv))
+    Q = SparseQuadraticForm(sparse(qi, qj, qv, n, n))
 
     α = read(fp["model"]["form"]["scale"])
     β = read(fp["model"]["form"]["offset"])

test/unit/library/formats.jl

@@ -178,6 +178,30 @@ function test_qubin_format()
                 @test _compare_models(src_model, dst_model)
             end
         end
+
+        # Test sparse array dimensions are preserved when some variables have no terms
+        @testset "sparse dimensions" begin
+            # Create a model where variable 3 has no linear or quadratic terms
+            # This tests that sparse(I, J, V, n, n) correctly sets dimensions
+            src_model = QUBOTools.Model{Int,Float64,Int}(
+                Set{Int}([1, 2, 3]),  # Explicitly include all 3 variables
+                Dict{Int,Float64}(1 => 1.0),  # Only variable 1 has linear term
+                Dict{Tuple{Int,Int},Float64}((1, 2) => 2.0);  # Only (1,2) quadratic term
+                sense  = :min,
+                domain = :bool,
+            )
+
+            temp_path = "$(tempname()).sparse_dim.qb"
+
+            QUBOTools.write_model(temp_path, src_model)
+
+            dst_model = QUBOTools.read_model(temp_path)
+
+            @test dst_model isa QUBOTools.Model
+            @test QUBOTools.dimension(dst_model) == 3  # Must preserve dimension n=3
+            @test QUBOTools.dimension(dst_model) == QUBOTools.dimension(src_model)
+            @test _compare_models(src_model, dst_model)
+        end
     end
 
     return nothing