[SDPA] Add missing negation of constant

Author: blegat

src/FileFormats/SDPA/SDPA.jl

@@ -190,7 +190,7 @@ function Base.write(io::IO, model::Model{T}) where {T}
         F0 = MOI.constant(func)
         for k in eachindex(F0)
             if !iszero(F0[k])
-                _print_entry(0, block, psd, k, F0[k])
+                _print_entry(0, block, psd, k, -F0[k])
             end
         end
         for term in func.terms
@@ -322,7 +322,7 @@ function Base.read!(io::IO, model::Model{T}) where T
             end
             if iszero(matrix)
                 if !iszero(coef)
-                    funcs[block].constants[k] += coef
+                    funcs[block].constants[k] -= coef
                 end
             else
                 if !iszero(coef)

test/FileFormats/SDPA/SDPA.jl

@@ -193,13 +193,13 @@ example_models = [
     ("example_A.sdpa", """
         variables: x, y
         minobjective: 10x + 20y
-        c1: [x + 1, 0, x + 2] in PositiveSemidefiniteConeTriangle(2)
-        c2: [5y + 3, 4y, 6y + 4] in PositiveSemidefiniteConeTriangle(2)
+        c1: [x + -1, 0, x + -2] in PositiveSemidefiniteConeTriangle(2)
+        c2: [5y + -3, 4y, 6y + -4] in PositiveSemidefiniteConeTriangle(2)
     """),
     ("example_B.sdpa", """
         variables: x
         minobjective: 1x
-        c1: [0, 2x + 2, 0] in PositiveSemidefiniteConeTriangle(2)
+        c1: [0, 2x + -2, 0] in PositiveSemidefiniteConeTriangle(2)
     """),
 ]
 @testset "Read and write/read $model_name" for (model_name, model_string) in example_models