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def sc_diff(x, a, b, period=None,
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""" sc_diff(x, a, b, period=2*pi) -> y
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Return (a,b)-sinh/cosh pseudo-derivative of a periodic sequence x.
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If x_j and y_j are Fourier coefficients of periodic functions x
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y_j = sqrt(-1)*sinh(j*a*2*pi/period)/cosh(j*b*2*pi/period) * x_j
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Defines the parameters of the sinh/cosh pseudo-differential
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The period of the sequence x. Default is 2*pi.
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sc_diff(cs_diff(x,a,b),b,a) == x
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``sc_diff(cs_diff(x,a,b),b,a) == x``