Tuesday, July 17, 2012

Redrawing Diagrams - Fun with Inkscape

Hand drawn curves
Good diagrams in publications are hard to come by and sometimes already published ones get re-used exactly due to the lack of the know-how on reproducing them. One classic example is the Entropy-Alpha space diagram produced by Cloud-Pottier. Though the diagram is simple enough and the space limit curves can be computed from the equations, it is sufficiently complex given no full recipe to warrant copying as-is. Copying with attribution is standard practice in science, but gives no insight into how the diagram was originally produced without contact with the authors or forensic analysis of the lines. The tell-tale randomness of the curves in this particular one makes me of the opinion that it was hand drawn, I will have to as Shane Cloude when I meet him over a beer in Munich.
Entropy/Alpha diagram

So I decided to try out my Inkscape skills and redraw the diagram from scratch using some theory and some free-hand approximations. Without definitive parametric equations for the bounding curves it is rather like trying to work out how the pyramids at Giza were built.

1 comment:

Patrick Imbo said...


All the ingredients of the recipe are available:
1) Have a look to matrix (21) from Cloude and Pottier paper,
2) proceed an eigen-value and eigen-vector analysis from these matrix,
3) a zest of analytical operation to obtains H(m) and alpha(m) equation for each validity domain,
4) plot with your favorite mathemetical tool