First of all, I wish everyone coming to this blog a happy new year ! Should this year be healthy and make your projects come true !
It’s been a while now since I published the code of my DeMIMOI core library. I had some time to make some improvements and add some more features to make it even more attractive to me, so possibly for anyone willing to give it a try too.
I thought well when I hoped this platform would help me easily build systems and make a bigger one by connecting smaller ones. I successfully managed to use the library with neural networks (special thanks to Accord.Net and AForge.Net). For example I made DeMIMOI models of a NARX (Nonlinear AutoRegressive eXogenous) neural network and a ARX regression model (AutoRegressive eXogenous).
These models can mimic almost any dynamic system mostly because they have a backward link that make their outputs at time t-1 one of their inputs.
Using the DeMIMOI library this backward link is easy to model and to code since it’s just a connection between an input and an output that, in code, is translated by a myModel.Outputs.ConnectTo(myModel.Inputs) for example. The data flow is then automatically managed by the DeMIMOI core.
I also started to put a database manager in a DeMIMOI model which can currently connect to a Mongo database. So I can save and retrieve data to build models or to act as some kind of a memory… Well it’s still in development now but the main features are already up ! I mean at least reading data from a pre-existing database. One step at a time right ?
To give you a better idea of what I’m talking about and what I’m doing, I’ll show you a picture of the system I’m currently working on.
First of all, let me just explain the background.
While coding the DeMIMOI ARX and NARX models, I wanted to build models that can learn the behavior of the servomotors of my AL5C robotic arm.
On a previous attempt last year, I had the arm moving freely and randomly while an application was recording at each time step the angle values from the potentiometers of each servo (thank you so much Phidgets !).
The results have been stored in a database that I can read using my DeMIMOI memory manager. Those data can then be sent to the ARX and NARX models, and also be used by the learner models to fit them to the servo behavior.
For this purpose, I coded the system which is described by the following diagram :
By the way, this image has been created using the GraphViz code that is automatically generated by the DeMIMOI collection that holds all the blocks of the system.
That’s a feature I’m quite proud of since it allows me to quickly check if what I coded is what I expected the system to be !
On the left of the diagram is the memory manager that reads the servo values from a Mongo database. The data produced is then fed to the ARX model and its teacher. They don’t need extra data processing, as opposed to the NARX model.
Indeed, the NARX model is made of a neural network that needs normalized data. That’s why you can see that the data coming from the memory block is also fed to a normalizer block that converts the raw data to a [-1, 1] range before being sent to the NARX and its teacher. Then the data coming out of the NARX model is denormalized to revert it back to its original data space.
On the ARX and NARX models you can clearly see the backward link that connects the output to the input. This link makes the network seamlessly recurrent. And again, in term of coding, it’s nothing harder than creating the link !
You also may have noticed the three probes that display some data values. This was for me to quickly check what are the model ouputs (simulated) compared to the real output (measured on the real system). On that run, the ARX is better than the NARX, but I currently didn’t push any analyze further to explain this…
My next work will now be focused on analyzing the results deeper, maybe working on the so called BPTT neural network (ouch ! it hurts !) or maybe even trying to make some kind of automated learning shell that would be able to test multiple models and parameters and then select the best one…
I know ! It seams like there’s going to be a huuuuge mountain to climb… I fight this feeling by telling me that I already climb quite a big part that it would be even worse to stop now !
I’ll let you know of my progress in a while. And do not hesitate to say hi or comment on this ! I’d be curious to know what it feels like for someone external !