# Only semi-explicit constant mass matrices are currently supported

**URL:** https://discourse.julialang.org/t/only-semi-explicit-constant-mass-matrices-are-currently-supported/67878
**Category:** New to Julia
**Tags:** question, package, diffeq
**Created:** [September 8, 2021, 3:29pm UTC](https://discourse.julialang.org/t/only-semi-explicit-constant-mass-matrices-are-currently-supported/67878 "2021-09-08T15:29:06Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![Akhilesh\_Raj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/akhilesh_raj/32/28921_2.png) [@Akhilesh\_Raj](https://discourse.julialang.org/u/Akhilesh_Raj)
#### Post date: [September 8, 2021, 3:29pm UTC](https://discourse.julialang.org/t/only-semi-explicit-constant-mass-matrices-are-currently-supported/67878/1 "2021-09-08T15:29:07Z")

</div>

Following is a sample code that I got from examples folder in the ModelingToolkit.jl. I added the last two lines to formulate the Problem. What are the possible reasons for the error in code " **Only semi-explicit constant mass matrices are currently supported. Faulty equation: source₊p₊v(t) ~ resistor₊p₊v(t).**". There are 26 states and 4 parameters whose default values were taken for the simulation.

```julia
include("electrical_components.jl")

@named source = ConstantVoltage(V=10.0)
@named resistor = Resistor(R=1.0)
@named inductor1 = Inductor(L=1.0e-2)
@named inductor2 = Inductor(L=2.0e-2)
@named ground = Ground()

eqs = [
       connect(source.p, resistor.p)
       connect(resistor.n, inductor1.p)
       connect(inductor1.n, inductor2.p)
       connect(source.n, inductor2.n, ground.g)
      ]

@named ll_model = ODESystem(eqs, t)
ll_model = compose(ll_model, [source, resistor, inductor1, inductor2, ground])
sys =ll_model

tspan = (0.0,100.0)
prob = ODEProblem(sys,[],tspan,[])

```