[Paparazzi-devel] Proposition for the Core developpers

[Arnault Ioualalen]

Hi,
I contact this mailing list on the advise that CheBuzz gives me on  
IRC, so that I could propose to the core developpers to test the  
numerical accuracy of their algorithms.

Let me explain that a little :
First I'm a phd student in Perpignan (France), my work concerns the  
numerical accuracy of floating-point calculations in embedded  
software. Mainly, my work is on the behalf of Airbus, and adresses the  
issue of rounding error propagation.

My point is, given
- a code written in some synchronous langage used in the industry  
(like LUSTRE),
- and the range of the inputs (of the sensors for example)
I can :
- calculate a safe over-approximation of the numerical error induce by  
the program
- propose automatically an equivalent program, this program is  
mathematically equivalent but has a better numerical accuracy (I won't  
enter into detail here because it's quite technical, but we already  
developped a tool call Sardana wich allow us to do it).

Ok, I hope I haven't lost you !
Remember just that each time you use floating-point arithmetics each  
value has a rounding error, and these rounding errors accumulate  
themselves during the whole process. Some very classical examples  
exist, where the rounding-errors became so big that the calculate  
value has nothing in common with the expected value.


I saw on your website (http://paparazzi.enac.fr/wiki) your "theory of  
operation" and the graphical representations of your control loops.
From what I could understand it's very much look like my kind of test  
data, so I'm gessing that (with some help) I could try to optimize,  
separatly, each control loop you have (or, perhaps, even together in  
one big piece of code).

My main problem is that I don't really understand what kind of value  
each variables could take, and your simulink-like representation may  
not be really complete.
Also, I would need some range of the inputs, or even better, a trace  
of a real execution of the code with the evolution of the values at  
each iteration.


If some core developpers are interested in my proposal, I can answer  
them over this email : address@hidden Or, if he lives  
in France (and more specifically in Toulouse) I can go there  
personnaly and meet him in person, that's not an issue (if it's not in  
Toulouse I could still arrange a trip to where he is, it's just little  
more time-consumming to organize).

To finish, I'll just want to say that your project could constitute an  
important example for my phd thesis and I'm really interested in  
working with your team over this topic of numerical accuracy.

Thanks for your answers (I hope there will be some), and sorry for  
this long email but it's never easy to make such a proposal in a few  
lines.


Arnault Ioualalen
Phd Student
DALI team - UPVD - LIRMM

ps: sorry for the possible orthographic errors, but it has been  
already a long day.