Hi, I am currently going through the DifferentialEquations documentation and am trying to run an example. Unfortunately, I am failing to achieve liftoff:

```
f = @ode_def_nohes LotkaVolterraTest begin
dx = a*x - b*x*y
dy = -c*y + d*x*y
end a=>1.5 b=1.0 c=3.0 d=1.0
u0 = [1.0;1.0]
tspan = (0.0,10.0)
prob = ODEProblem(f,u0,tspan)
```

Gives:

`UndefVarError: @ode_def_nohes not defined`

I don’t really understand this type of function declaration, so I am not sure how to tweak it appropriately (besides just rewriting the DE in the “standard” way).

Any explanations would be greatly appreciated.

Thanks,

DS