Draw the graph of y = sin (1/x) for |x| < 1. Color blue the regions inside the graph where y is positive, and red those where it is negative.

The basic way to draw a graph of a function is by drawing it as a sequence of small lines between (x, f(x)) and (x+dx, f(x+dx)). There are several things that make this graph not quite ordinary. The function 1/x is singular at 0, so you cannot just graph an entire interval through 0, and must plot left and right separately. But then the graph oscillates at a higher and higher frequency as it gets close to x=0, with period decreasing below any fixed size. This requires that the interval dx decrease as the graph gets closer to 0.

How should it be chosen? Roughly speaking, the number of lines in each loop of the graph should remain constant, say N = 100. The graph crosses the x-axis at the points 1/ π n, so one loop lasts between 1/ π n and 1/ π (n+1). What the program belwo does is plot each loop separately. Another possible solution would be to set dx = x²/N, since 1/ π n - 1/ π (n+1) = 1/ π n(n+1) which is roughly proportional to x² if x = 1/ π n. (This is not what I thought originally.) Doing this makes it easy to color alternate loops in different colors.

sinx.py