Add error message for Matrix ± AbstractJuMPScalar (#3557)

src/operators.jl

@@ -451,3 +451,23 @@ function LinearAlgebra.issymmetric(x::Matrix{T}) where {T<:_JuMPTypes}
     end
     return true
 end
+
+function Base.:+(A::AbstractMatrix, x::AbstractJuMPScalar)
+    return error(
+        "Addition between a Matrix and a JuMP variable is not supported: instead of `A + x`, " *
+        "do `A .+ x` for element-wise addition, or if you are modifying the diagonal entries of the matrix " *
+        "do `A + x * LinearAlgebra.I(n)`, where `n` is the diagonal length.",
+    )
+end
+
+Base.:+(x::AbstractJuMPScalar, A::AbstractMatrix) = A + x
+
+function Base.:-(A::AbstractMatrix, x::AbstractJuMPScalar)
+    return error(
+        "Subtraction between a Matrix and a JuMP variable is not supported: instead of `A - x`, " *
+        "do `A .- x` for element-wise subtraction, or if you are modifying the diagonal entries of the matrix " *
+        "do `A - x * LinearAlgebra.I(n)`, where `n` is the diagonal length.",
+    )
+end
+
+Base.:-(x::AbstractJuMPScalar, A::AbstractMatrix) = A - x

test/test_operator.jl

@@ -625,4 +625,43 @@ function test_complex_pow()
     return
 end
 
+function test_matrix_abstractscalar_add()
+    model = Model()
+    @variable(model, x)
+    A = rand(Float64, 2, 2)
+    @test_throws(
+        ErrorException(
+            "Addition between a Matrix and a JuMP variable is not supported: instead of `A + x`, " *
+            "do `A .+ x` for element-wise addition, or if you are modifying the diagonal entries of the matrix " *
+            "do `A + x * LinearAlgebra.I(n)`, where `n` is the diagonal length.",
+        ),
+        A + x
+    ),
+    @test_throws(
+        ErrorException(
+            "Addition between a Matrix and a JuMP variable is not supported: instead of `A + x`, " *
+            "do `A .+ x` for element-wise addition, or if you are modifying the diagonal entries of the matrix " *
+            "do `A + x * LinearAlgebra.I(n)`, where `n` is the diagonal length.",
+        ),
+        x + A
+    ),
+    @test_throws(
+        ErrorException(
+            "Subtraction between a Matrix and a JuMP variable is not supported: instead of `A - x`, " *
+            "do `A .- x` for element-wise subtraction, or if you are modifying the diagonal entries of the matrix " *
+            "do `A - x * LinearAlgebra.I(n)`, where `n` is the diagonal length.",
+        ),
+        A - x
+    ),
+    @test_throws(
+        ErrorException(
+            "Subtraction between a Matrix and a JuMP variable is not supported: instead of `A - x`, " *
+            "do `A .- x` for element-wise subtraction, or if you are modifying the diagonal entries of the matrix " *
+            "do `A - x * LinearAlgebra.I(n)`, where `n` is the diagonal length.",
+        ),
+        x - A
+    ),
+    return
+end
+
 end