godesim
Simulate complex systems with a simple API.
Wrangle non-linear differential equations while writing maintainable, simple code.
Why Godesim?
ODE solvers seem to fill the niche of simple system solvers in your numerical packages such as scipy's odeint/solve_ivp.
Among these integrators there seems to be room for a solver that offers simulation interactivity such as modifying the differential equations during simulation based on events such as a rocket stage separation.
Installation
Requires Go.
go get github.com/soypat/godesimProgress
Godesim is in early development and will naturally change as it is used more. The chart below shows some features that are planned or already part of godesim.
| Status legend | Planned | Started | Prototype | Stable | Mature |
|---|---|---|---|---|---|
| Legend symbol |
| Features | Status | Notes |
|---|---|---|
| Non-linear solvers | Suite of ODE solvers available. | |
| Non-autonomous support | U vector which need not a defined differential equation like X does. |
|
| Event driver | Eventer interface implemented. | |
| Stiff solver | Newton-Raphson algorithm implemented and tested. |
Algorithms available and benchmarks
| Algorithm | Time/Operation | Memory/Op | Allocations/Op |
|---|---|---|---|
| RK4 | 1575 ns/op | 516 B/op | 12 allocs/op |
| RK5 | 2351 ns/op | 692 B/op | 21 allocs/op |
| RKF45 | 3229 ns/op | 780 B/op | 25 allocs/op |
| Newton-Raphson | 8616 ns/op | 4292 B/op | 92 allocs/op |
| Dormand-Prince | 4365 ns/op | 926 B/op | 32 allocs/op |
Examples
Quadratic Solution
// Declare your rate-of-change functions using state-space symbols
Dtheta := func(s state.State) float64 {
return s.X("theta-dot")
}
DDtheta := func(s state.State) float64 {
return 1
}
// Set the Simulation's differential equations and initial values and hit Begin!
sim := godesim.New() // Configurable with Simulation.SetConfig(godesim.Config{...})
sim.SetDiffFromMap(map[state.Symbol]state.Diff {
"theta": Dtheta,
"theta-dot": DDtheta,
})
sim.SetX0FromMap(map[state.Symbol]float64{
"theta": 0,
"theta-dot": 0,
})
sim.SetTimespan(0.0, 1.0, 10) // One second simulated
sim.Begin()The above code solves the following system:
for the domain t=0 to t=1.0 in 10 steps where theta and theta-dot are the X variables. The resulting curve is quadratic as the solution for this equation (for theta and theta-dot equal to zero) is
How to obtain results
// one can then obtain simulation results as float slices
t := sim.Results("time")
theta := sim.Results("theta")Other examples
To run an example, navigate to it's directory (under examples) then type go run . in console.
There are three simple examples which have been cooked up and left in _examples directory.
I've been having problems running Pixel on my machine so the simulation animations are still under work.
Final notes
Future versions of gonum will have an ODE solver too. Ideally godesim would base it's algorithms on gonum's implementation. See https://github.com/gonum/exp ode package.
Contributing
Pull requests welcome!
This is my first library written for any programming language ever. I'll try to be fast on replying to pull-requests and issues.