Apply Gaussian smearing to spectrum y value.

        Args:
            sigma: Std dev for Gaussian smear function

def smear(self, sigma):
        """
        Apply Gaussian smearing to spectrum y value.

        Args:
            sigma: Std dev for Gaussian smear function
        """
        diff = [self.x[i + 1] - self.x[i] for i in range(len(self.x) - 1)]
        avg_x_per_step = np.sum(diff) / len(diff)
        if len(self.ydim) == 1:
            self.y = gaussian_filter1d(self.y, sigma / avg_x_per_step)
        else:
            self.y = np.array([
                gaussian_filter1d(self.y[:, k], sigma / avg_x_per_step)
                for k in range(self.ydim[1])]).T