function dispersion_vector = getDispersionVector(N, D, ref_zdw, randomize_ZDW, randomkey)
% s.MATLAB version of the Python generator shown above.
% Returns an N×1 vector (ps/(nm·km)).
%
% D is the nominal dispersion magnitude. For D>0 the link is segmented with
% alternating sign (+D, -D, +D, …). For D==0 it is flat (0) except for
% ZDW randomization. The ZDW detuning is ~N(0, 2 nm) around 1310 nm and is
% converted to dispersion via 0.09 ps/(nm·km) per nm.

    % constants (matching the Python code)
    meanLambda_nm = 1310;        % center wavelength
    sigma_nm      = 2;           % ZDW sigma
    Dslope        = 0.07;        % ps/(nm·km) per nm detuning

    % random ZDW-induced dispersion offset
    if randomize_ZDW
        rng(randomkey, 'twister');
        rand_zdws_nm = meanLambda_nm + sigma_nm .* randn(N,1);
        rand_D = (rand_zdws_nm - ref_zdw) .* Dslope;   % ps/(nm·km)
    else
        rand_D = zeros(N,1);
    end

    % nominal segmented pattern (match Python intent; keep length N)
    if D > 0
        base = (-1) .^ ((0:N-1).');   % +1,-1,+1,-1,...
    else % D == 0 (or anything else)
        base = ones(N,1);
    end

    dispersion_vector = base .* D + rand_D;  % ps/(nm·km)
end