Plotting two functions simultaneously with matplotlib

Question

basically I want to graph two functions

g1 = x*cos(x*pi)
g2 = 1 - 0.6x^2

and then plot the intersection, I already have a module that takes inputs close to the two lines intersections, and then converges to those points (there's four of them)

but I want to graph these two functions and their intersections using matplotlib but have no clue how. I've only graphed basic functions. Any help is greatly appreciated

Answer 1

Assuming you can get as far as plotting one function, with x and g1 as numpy arrays,

pylab.plot(x,g1)

just call plot again (and again) to draw any number of separate curves:

pylab.plot(x,g2)

finally display or save to a file:

pylab.show()

To indicate a special point such as an intersection, just pass in scalars for x, y and ask for a marker such 'x' or 'o' or whatever else you like.

pylab.plot(x_intersect, y_intersect, 'x', color="#80C0FF")

Alternatively, I often mark a special place along x with a vertical segment by plotting a quick little two-point data set:

pylab.plot( [x_special, x_special], [0.5, 1.9], '-b' )

I may hardcode the y values to look good on a plot for my current project, but obviously this is not reusable for other projects. Note that plot() can take ordinary python lists; no need to convert to numpy arrays.

If you can't get as far as plotting one function (just g1) then you need a basic tutorial in matplot lib, which wouldn't make a good answer here but please go visit http://matplotlib.org/ and google "matplotlib tutorial" or "matplotlib introduction".