Merge pull request #1163 from SciML/nonlinear

automatically put nonlinear systems in canonical form

Author: ChrisRackauckas

src/systems/nonlinear/nonlinearsystem.jl

@@ -65,7 +65,9 @@ function NonlinearSystem(eqs, states, ps;
                          systems=NonlinearSystem[],
                          connection_type=nothing,
                          )
-    eqs = collect(eqs)
+    # Move things over, but do not touch array expressions
+    eqs = [0 ~ x.rhs - x.lhs for x in collect(eqs)]
+
     if !(isempty(default_u0) && isempty(default_p))
         Base.depwarn("`default_u0` and `default_p` are deprecated. Use `defaults` instead.", :NonlinearSystem, force=true)
     end

test/nonlinearsystem.jl

@@ -37,8 +37,8 @@ end
 
 # Define a nonlinear system
 eqs = [0 ~ σ*(y-x),
-       0 ~ x*(ρ-z)-y,
-       0 ~ x*y - β*z]
+       y ~ x*(ρ-z),
+       β*z ~ x*y]
 ns = NonlinearSystem(eqs, [x,y,z], [σ,ρ,β])
 jac = calculate_jacobian(ns)
 @testset "nlsys jacobian" begin
@@ -156,4 +156,3 @@ end
     @test isequal(union(Set(states(sys1)), Set(states(sys2))), Set(states(sys3)))
     @test isequal(union(Set(equations(sys1)), Set(equations(sys2))), Set(equations(sys3)))
 end
-