In fact, i want to have 2 vertical axis (or more) because I have to plot two line graphs. Both of them are in function of the position x, and vertical axes are in range :
 first one from 1.0E00 to 1.0E01
 and the second one from 8.0E08 to 1.0E06
So that with the second graph, I see a line...
That is why I want to dissociate each Y axis
