Fix some issues with fix! (#294)

* Fix multiply divide's treatment of ConstVexity() variables

* Add test

* Move test, add test for 228

* remove extra newline

src/atoms/affine/multiply_divide.jl

@@ -80,13 +80,13 @@ function conic_form!(x::MultiplyAtom, unique_conic_forms::UniqueConicForms=Uniqu
             objective = const_multiplier * objective
 
         # left matrix multiplication
-        elseif x.children[1].head == :constant
+        elseif vexity(x.children[1]) == ConstVexity()
             objective = conic_form!(x.children[2], unique_conic_forms)
-            objective = kron(sparse(1.0I, x.size[2], x.size[2]), x.children[1].value) * objective
+            objective = kron(sparse(1.0I, x.size[2], x.size[2]), evaluate(x.children[1])) * objective
         # right matrix multiplication
         else
             objective = conic_form!(x.children[1], unique_conic_forms)
-            objective = kron(transpose(x.children[2].value), sparse(1.0I, x.size[1], x.size[1])) * objective
+            objective = kron(transpose(evaluate(x.children[2])), sparse(1.0I, x.size[1], x.size[1])) * objective
         end
         cache_conic_form!(unique_conic_forms, x, objective)
     end
@@ -158,7 +158,7 @@ function conic_form!(x::DotMultiplyAtom, unique_conic_forms::UniqueConicForms=Un
         # promote the size of the coefficient matrix, so eg
         # 3 .* x
         # works regardless of the size of x
-        coeff = x.children[1].value .* ones(size(x.children[2]))
+        coeff = evaluate(x.children[1]) .* ones(size(x.children[2]))
         # promote the size of the variable
         # we've previously ensured neither x nor y is 1x1
         # and that the sizes are compatible,

test/runtests.jl

@@ -34,6 +34,7 @@ push!(solvers, SCSSolver(verbose=0, eps=1e-6))
 
 @testset "Convex" begin
     include("test_utilities.jl")
+    include("test_const.jl")
     include("test_affine.jl")
     include("test_lp.jl")
     include("test_socp.jl")

test/test_const.jl

@@ -0,0 +1,35 @@
+@testset "Constant variables: $solver" for solver in solvers
+
+    @testset "Issue #166" begin
+        # Issue #166
+        α = Variable(5)
+        fix!(α, ones(5,1))
+
+        # has const vexity, but not at the head
+        c = (rand(5,5) * α) * ones(1,5) 
+
+        β = Variable(5)
+        β.value = ones(5)
+
+        problem = minimize(sum(c * β), [β >= 0])
+        solve!(problem, solver)
+        @test problem.optval ≈ evaluate(sum(c * β)) atol=TOL
+        @test problem.optval ≈ 0.0 atol=TOL
+        @test β.value ≈ zeros(5) atol=TOL
+    end
+
+    @testset "Issue #228" begin
+        x = Variable(2)
+        y = Variable(2)
+        fix!(x, [1 1]')
+        prob = minimize(y'*(x+[2 2]'), [y>=0])
+        solve!(prob, solver)
+        @test prob.optval ≈ 0.0 atol = TOL
+
+        prob = minimize(x'*y, [y>=0])
+        solve!(prob, solver)
+        @test prob.optval ≈ 0.0 atol = TOL
+    end
+
+
+end