How could I hatch the oscillation
Here is my ggb file.
I want to shadow the region of uppersum-lowersum, in order to indicating the oscillation of integrand function f along the interval [a,b]. I do not know how to do so. At present, what I can do is just to draw the target parallelgram, and then to fill it with hatch. But the task is so boring. Maybe there is some easy way to do so. Can anyone help me?