fixup symbolic: vech

Author: Alexey Stukalov

src/implied/RAM/symbolic.jl

@@ -198,7 +198,10 @@ end
 function eval_Σ_symbolic(S, I_A⁻¹, F; vech::Bool = false, simplify::Bool = false)
     Σ = F * I_A⁻¹ * S * permutedims(I_A⁻¹) * permutedims(F)
     Σ = Array(Σ)
-    vech && (Σ = SEM.vech(Σ))
+    if vech
+        n = size(Σ, 1)
+        Σ = [Σ[i, j] for j in 1:n for i in j:n]
+    end
     if simplify
         Threads.@threads for i in eachindex(Σ)
             Σ[i] = Symbolics.simplify(Σ[i])