You have to figure out the crossing points. Once you have figured out the x that they have in common, then you can trapz() one, minus trapz() the other, to get the area between.
You would then also be able to use fill() . The trick there is to construct
XF = [first_x_ascending_order, fliplr(second_x_ascending_order)]
YF = [first_y_in_x_order, fliplr(second_y_in_x_order)];
fill(XF, YF)
That is, you want a line that goes along the first x, then backwards along the second x, so that you get back to the common origin.
