# [SciPy-User] How to find the intersections between two lines

seasoul bioseasoul@gmail....
Thu Apr 8 23:15:37 CDT 2010

```This is my first post in the mailing list.
I want to find the intersections between two lines. One line is an arbitrary
straight line, the other is a fitting line created by a interpolation
procedure.
Below is a simple code:

x = linspace(0,10,20)
y = rand(20)*10
plt.plot(x,y,'o')
f = interpolate.interp1d(x,y,kind=5)
xx = linspace(0,10,100)
yy = f(xx)
plt.plot(xx,yy,'r-')
y2 = x
plt.plot(x,y2,'b-')
def func(x):
out = [x[1]-x[0]]
out.append(x[1]-f(x[0]))
return out
fsolve(func,[1,1])

The fitting line is a polynomial curve, the straight line is y=x. This
function can only find one of the intersection points,not all.

I tried to use x[:,1] and x[:,2], and hope in the function func, the
operation is element-by-element, but some errors came out.
Any help is appreciated.

The output figure:

http://picasaweb.google.com/lh/photo/vJZRP6tAmmhpIh4J2BG0-g?feat=directlink
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```

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