Merge pull request #540 from SciML/myb/fix

Convert user supplied independent variable to Variable and better err…

Author: ChrisRackauckas

src/systems/abstractsystem.jl

@@ -188,7 +188,7 @@ end
 namespace_operation(O::Constant,name,ivname) = O
 
 independent_variable(sys::AbstractSystem) = sys.iv
-states(sys::AbstractSystem) = isempty(sys.systems) ? setdiff(sys.states, convert.(Variable,sys.pins)) : [sys.states;reduce(vcat,namespace_variables.(sys.systems))]
+states(sys::AbstractSystem) = unique(isempty(sys.systems) ? setdiff(sys.states, convert.(Variable,sys.pins)) : [sys.states;reduce(vcat,namespace_variables.(sys.systems))])
 parameters(sys::AbstractSystem) = isempty(sys.systems) ? sys.ps : [sys.ps;reduce(vcat,namespace_parameters.(sys.systems))]
 pins(sys::AbstractSystem) = isempty(sys.systems) ? sys.pins : [sys.pins;reduce(vcat,namespace_pins.(sys.systems))]
 function observed(sys::AbstractSystem)

src/systems/diffeqs/abstractodesystem.jl

@@ -79,7 +79,7 @@ function calculate_massmatrix(sys::AbstractODESystem; simplify=true)
             j = findfirst(x->isequal(x.name,var_from_nested_derivative(eq.lhs)[1].name),dvs)
             M[i,j] = 1
         else
-            error("Only semi-explicit constant mass matrices are currently supported")
+            error("Only semi-explicit constant mass matrices are currently supported. Faulty equation: $eq.")
         end
     end
     M = simplify ? ModelingToolkit.simplify.(M) : M

src/systems/diffeqs/odesystem.jl

@@ -100,6 +100,8 @@ function ODESystem(eqs, iv=nothing; kwargs...)
                 break
             end
         end
+    else
+        iv = convert(Variable, iv)
     end
     iv === nothing && throw(ArgumentError("Please pass in independent variables."))
     for eq in eqs

test/mass_matrix.jl

@@ -9,7 +9,7 @@ eqs = [D(y[1]) ~ -k[1]*y[1] + k[3]*y[2]*y[3],
        0 ~  y[1] + y[2] + y[3] - 1]
 
 sys = ODESystem(eqs,t,y,k)
-@test_throws ArgumentError ODESystem(eqs,y)
+@test_throws ArgumentError ODESystem(eqs,y[1])
 M = calculate_massmatrix(sys)
 @test M == [1 0 0
             0 1 0