English: Consecutive partial sums of the first 5 Fourier series components of a square wave. These can be thought of as the output of a perfect low-pass filter of progressively higher cutoff frequency to a square wave input. They illustrate the Gibbs phenomenon; at the edges of the square wave, as more terms of the Fourier series are added, the amount of the overshoot does not approach zero, but converges to the function by being "pinched" into a vanishingly small interval at the edge. Created with pgf/tikz and Adobe Photoshop