Allow for AbstractMathProfSolver in Settings

src/Orbit-wise.jl

@@ -10,7 +10,7 @@ immutable Settings
    S::Vector
    AutS::Group
    radius::Int
-   solver::SCSSolver
+   solver::AbstractMathProgSolver
    upper_bound::Float64
    tol::Float64
 end
@@ -166,8 +166,10 @@ function init_model(Uπs)
 
     for k in 1:l
         s = size(Uπs[k],2)
-        P[k] = JuMP.@variable(m, [i=1:s, j=1:s])
-        JuMP.@SDconstraint(m, P[k] >= 0.0)
+        if s > 0
+           P[k] = JuMP.@variable(m, [i=1:s, j=1:s])
+           JuMP.@SDconstraint(m, P[k] >= 0.0)
+        end
     end
 
     JuMP.@variable(m, λ >= 0.0)