In above equations, T0 is the base period and f0 is base frequency accordingly. In the above definition, t0 is the (pseudo) start time of the step in which the amplitude is defined.
Syntax
amplitude Sine (1) (2) (3) [(4)...]
amplitude Cosine (1) (2) (3) [(4)...]
# (1) int, unique tag
# (2) double, base period T_0
# (3) double, amplitude at base period/frequency a_0
# [(4)...] double, optional amplitudes at higher periods a_i