function result = gauss_beam1D(x0, xdata)
% x0(1) = offset
% x0(2) = amplitude
% x0(3) = x centroid location
% x0(4) = x width

result = x0(1) + x0(2).*exp(-2.0.*( ...
                           ((xdata - x0(3)).^2)/(x0(4).^2)));