You might think that calculating intersection points is pretty
trivial but there are complications in computing that you don't
get in math
<H2>2 straight lines</H2>
If you run
x=[1 2 3]
y1=[ 0 1 2]
y2=[2 1 0]
plot(x,y1,x,y2)
you'll see that the lines cross at x=2, y=1. Using maths
we could
<UL>
<LI>Find eq of lines and solve
x-y=1
-x+y=2


<LI>x(y1-y2==0) - good because it can find lots of points.
x=1:10
y1=4+(-1).^x
y2=ones(1,10)*5
plot(x,y1,x,y2) 
x(y1-y2==0)    prints the x values where the y values are the same
</UL>

<H2>Problem 1: precision</H2>


<H2>Problem 2: precision - close lines</H2>


<H2>Problem 3: intersection not at a datapoint</H2>
x=1:10
y1=sin(x)
y2=cos(x)
plot(x,y1,x,y2)

You'll see that the lines clearly cross twice, but they don't
cross at one of the plotted points, so y1-y2 is never 0.

We need to interpolate the values, but to do that we need to 
make assumptions about the nature of the data - should the points ...
be connected by straight lines or curves? If curves, what type?

In general the data's likely to come from an experiment. If the 
2 sets of data don't share the same same of xcoordinates there are
further complications.