//  [python]
def _f02sine(self, f0_values):
        """ f0_values: (batchsize, length, dim)
            where dim indicates fundamental tone and overtones
        """
        # convert to F0 in rad. The interger part n can be ignored
        # because 2 * np.pi * n doesn't affect phase
        rad_values = (f0_values / self.sampling_rate) % 1

        # initial phase noise (no noise for fundamental component)
        rand_ini = torch.rand(f0_values.shape[0], f0_values.shape[2], \
                              device=f0_values.device)
        rand_ini[:, 0] = 0
        rad_values[:, 0, :] = rad_values[:, 0, :] + rand_ini

        # instantanouse phase sine[t] = sin(2*pi \sum_i=1 ^{t} rad)
        if not self.flag_for_pulse:
#             # for normal case

#             # To prevent torch.cumsum numerical overflow,
#             # it is necessary to add -1 whenever \sum_k=1^n rad_value_k > 1.
#             # Buffer tmp_over_one_idx indicates the time step to add -1.
#             # This will not change F0 of sine because (x-1) * 2*pi = x * 2*pi
#             tmp_over_one = torch.cumsum(rad_values, 1) % 1
#             tmp_over_one_idx = (padDiff(tmp_over_one)) < 0
#             cumsum_shift = torch.zeros_like(rad_values)
#             cumsum_shift[:, 1:, :] = tmp_over_one_idx * -1.0

#             phase = torch.cumsum(rad_values, dim=1) * 2 * np.pi
            rad_values = t.nn.functional.interpolate(rad_values.transpose(1, 2), 
                                                         scale_factor=1/self.upsample_scale, 
                                                         mode="linear").transpose(1, 2)
    
#             tmp_over_one = torch.cumsum(rad_values, 1) % 1
#             tmp_over_one_idx = (padDiff(tmp_over_one)) < 0
#             cumsum_shift = torch.zeros_like(rad_values)
#             cumsum_shift[:, 1:, :] = tmp_over_one_idx * -1.0
    
            phase = torch.cumsum(rad_values, dim=1) * 2 * np.pi
            phase = t.nn.functional.interpolate(phase.transpose(1, 2) * self.upsample_scale, 
                                                    scale_factor=self.upsample_scale, mode="linear").transpose(1, 2)
            sines = torch.sin(phase)
            
        else:
            # If necessary, make sure that the first time step of every
            # voiced segments is sin(pi) or cos(0)
            # This is used for pulse-train generation

            # identify the last time step in unvoiced segments
            uv = self._f02uv(f0_values)
            uv_1 = torch.roll(uv, shifts=-1, dims=1)
            uv_1[:, -1, :] = 1
            u_loc = (uv < 1) * (uv_1 > 0)

            # get the instantanouse phase
            tmp_cumsum = torch.cumsum(rad_values, dim=1)
            # different batch needs to be processed differently
            for idx in range(f0_values.shape[0]):
                temp_sum = tmp_cumsum[idx, u_loc[idx, :, 0], :]
                temp_sum[1:, :] = temp_sum[1:, :] - temp_sum[0:-1, :]
                # stores the accumulation of i.phase within
                # each voiced segments
                tmp_cumsum[idx, :, :] = 0
                tmp_cumsum[idx, u_loc[idx, :, 0], :] = temp_sum

            # rad_values - tmp_cumsum: remove the accumulation of i.phase
            # within the previous voiced segment.
            i_phase = torch.cumsum(rad_values - tmp_cumsum, dim=1)

            # get the sines
            sines = torch.cos(i_phase * 2 * np.pi)
        return sines