title: How to find intersection point of a plot with x-axis in python?
body: <p>I want to get the intersection point of a curve I plotted with the x-axis.
  I don't have the equation of the curve. I only have the discrete values and I plotted them. Is there a way to do this easily with python?
  The code is simple:</p>
  
  <pre><code>    incident_angles = np.linspace(0,90,91)
      r_p = np.array(r_p_list) 
      #r_p_list contains fresnel coefficients for the incident angles
      py.plot(incident_angles,abs(r_p))
  </code></pre>
  
  <p>Now when I plot this, the curve intersects with the x-axis at a point which is the brewster angle. I want to get this point. 
  The graph should look like the blue curve in this image:
  <a href="http://physics-animations.com/Physics/English/raysfig2.gif" rel="nofollow">fresnel coefficients for reflected TM polarized light</a>
  Thanks</p>