Why does FourierSeries[] return the input?

[rroger (Roger Backhus)]

Why doesn’t this work?

freq = 10.0*^6

FourierSeries[SquareWave[freq*t], t, 5]

All Mathematica does is throw my expression back at me.

Thanks.

[gianlucagorni]

Perhaps the frequency is too high and there is trouble splitting the interval into so many subintervals. Compare

PiecewiseExpand[SquareWave[10*t], 0 < t < 2 Pi]
PiecewiseExpand[SquareWave[20*t], 0 < t < 2 Pi]

[rohitnamjoshi]

Perhaps because the frequency is so high that 5 terms are insufficient?

s[t_] := FourierSinSeries[SquareWave[t], t, 5, FourierParameters -> {1, 2 Pi}];

Plot[Evaluate@fs[t], {t, 0, 2 Pi}]