Hello,

I shall pretense this with that I am very new to ModelingToolkit

As part of a bigger system I have a laser source term which chnages based on the type of a struct defining the equation. This means that I want to build a function that defines the laser based on type and make this a modeling toolkit model to the implement elsewhere in my equations. However this equation isn’t a D(t) but rather a f(t) equation. Is there a way to make modeling toolkit solve these without differentiating? Currently when I use structural_simply(eq) the equation just disappears.

Here is a rough MWE that simulates this and matches my usecase without the multiple dispatch on types.

```
function test_eq(;name)
@parameters a b
@variables y(t)
eqs = [y ~ a*t + b]
ODESystem(eqs,t;name)
end
@named testeq=test_eq()
testsimp=structural_simplify(testeq)
```

After you run structural_simplify, the whole equation vanishes as I guess it isn’t a differential equation but I’m not sure.

Thanks for any help