[Bridges] fix modify MultirowChange for Constraint.SetMap (#2662)

Author: odow

src/Bridges/Constraint/set_map.jl

@@ -262,14 +262,20 @@ end
 function MOI.modify(
     model::MOI.ModelLike,
     bridge::BT,
-    change::MOI.MultirowChange,
-) where {BT<:MultiSetMapBridge}
+    change::MOI.MultirowChange{T},
+) where {T,BT<:MultiSetMapBridge{T}}
     # It is important here that `change.new_coefficients` contains the complete
     # new sparse column associated to the variable. Calling modify twice with
     # part of the column won't work since  the linear map might reset all the
     # column each time.
-    coefficients = MOI.Bridges.map_function(BT, change.new_coefficients)
-    new_change = MOI.MultirowChange(change.variable, coefficients)
+    n = MOI.dimension(MOI.get(model, MOI.ConstraintSet(), bridge.constraint))
+    dense = zeros(T, n)
+    for (row, value) in change.new_coefficients
+        dense[row] += value
+    end
+    map_dense = MOI.Bridges.map_function(BT, dense)
+    sparse = Tuple{Int64,T}[rv for rv in enumerate(map_dense) if !iszero(rv[2])]
+    new_change = MOI.MultirowChange(change.variable, sparse)
     MOI.modify(model, bridge.constraint, new_change)
     return
 end

test/Bridges/Constraint/NormOneConeToNormConeBridge.jl

@@ -65,6 +65,25 @@ function test_runtests_norm_inf()
     )
     return
 end
+
+function test_modify_MultirowChange()
+    inner = MOI.Utilities.Model{Float64}()
+    model = MOI.Bridges.Constraint.NormOneConeToNormCone{Float64}(inner)
+    x = MOI.add_variables(model, 2)
+    f = MOI.Utilities.vectorize(1.0 .* x)
+    c = MOI.add_constraint(model, f, MOI.NormOneCone(2))
+    @test ≈(
+        MOI.get(model, MOI.ConstraintFunction(), c),
+        MOI.Utilities.vectorize([1.0 * x[1], 1.0 * x[2]]),
+    )
+    MOI.modify(model, c, MOI.MultirowChange(x[2], [(2, 2.0)]))
+    @test ≈(
+        MOI.get(model, MOI.ConstraintFunction(), c),
+        MOI.Utilities.vectorize([1.0 * x[1], 2.0 * x[2]]),
+    )
+    return
+end
+
 end  # module
 
 TestConstraintNormSpecialCase.runtests()