# [SciPy-User] calculating intersection points in probability curves

Tim Michelsen timmichelsen@gmx-topmail...
Tue Mar 2 15:56:35 CST 2010

```Hello,
I am performing a curve fit and also showing a distribution histogram
envelope in my plot.

In order to help the reader to evaluate the result I would like to draw
certain
boundaries (vertical and horizontal lines).
While I am aware on how to draw such lines with matplotlib, I would like
to know whether there
are some functions in scipy or matplotlib which help me to retrieve the
coordinates

a) at which two curves intersect
b) at which a distribution reaches a certain value?

Example:
How do I get the y-axis value which is reached by the green curve in
http://matplotlib.sourceforge.net/_images/histogram_demo_extended_021.png
at a x-axis value of in 175?

I could proably use a solver from numpy like
http://docs.scipy.org/doc/numpy/reference/generated/numpy.linalg.solve.html#numpy.linalg.solve
but if I plot a distribution, the equation of the envelove is unknown at the
first place.

I'd appreciate your help or pointers to examples.