HP (Hewlett-Packard) 50g ユーザーズマニュアル

Page 16-38

From the plot it is very difficult to distinguish the original function from the 
Fourier series approximation.  Using k = 2, or 5 terms in the series, shows not so 
good a fitting:

     

The Fourier series can be used to generate a periodic triangular wave (or saw 
tooth wave) by changing the horizontal axis range, for example, from –2 to 4. 
The graph shown below uses k = 5:

A square wave can be generated by using the function

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