build_function needs vector of independent variables

[baggepinnen]

When building a function with a CTarget I noticed that

MethodError: no method matching get_varnumber(::Operation, ::Variable{ModelingToolkit.Parameter{Number}})
Closest candidates are:
  get_varnumber(::Operation, !Matched::Array{Operation,1}) at /home/fredrikb/.julia/dev/ModelingToolkit/src/build_function.jl:463
  get_varnumber(::Operation, !Matched::Array{var"#s254",1} where var"#s254"<:Variable) at /home/fredrikb/.julia/dev/ModelingToolkit/src/build_function.jl:464
in include_string at base/loading.jl:1088

It works if I provide a vector of independent variables, but it would be nice if I could provide just time.

Example:

using OrdinaryDiffEq, ModelingToolkit
controller(t) = cos((t+5)^2)
function dynamics(dx, x, p, t)
      k, k₃, Jₘ, Jₐ, c, fa, tx = p
      q, θ, q̇, θ̇ = x

      u     = controller(t)
      Δq    = q - θ
      Δv    = q̇ - θ̇
      dx[1] = q̇
      dx[2] = θ̇
      dx[3] = -(k * Δq + k₃ * Δq^3 + c * Δv) + tx*u
      dx[4] =   k * Δq + k₃ * Δq^3 + c * Δv - fa*tanh(1000θ̇)

      dx[3] /= Jₘ
      dx[4] /= Jₐ
end


x0 = Float64[0, 0, 0, 0]
tspan = (0.0, 70)
p = [18e3, 10, 10, 3, 9, 100, 1000]
prob = ODEProblem(dynamics, x0, tspan, p)

@register controller(t)

sys = modelingtoolkitize(prob)
rhs = getfield.(sys.eqs, :rhs)


ccode = build_function(
      sys.eqs,
      states(sys),
      parameters(sys),
      [independent_variable(sys)], # I had to wrap this in a vector <------------------------------------------------------
      target = ModelingToolkit.CTarget(),
      lhsname = :dx,
      rhsnames = [:x, :params, :t],
)

[ChrisRackauckas]

Interesting. The tests don't have to specify it as a vector: https://github.com/SciML/ModelingToolkit.jl/blob/master/test/build_targets.jl.

rhsnames = [:x, :params, :t], that's incorrect: it should be the vector of names, i.e. [[u1,u2,u3,...],[p1,p2,p3...],t]

[ChrisRackauckas]

This was fixed up in JuliaSymbolics/Symbolics.jl#72