SystemModling/Work 1/scripts/sample_data.m

function sample_data(t, x, Ts, A0, omega, filename)
% SAMPLE_DATA - Resamples pendulum simulation data and exports to CSV
%
% Usage:
%   sample_pendulum_data(t, x, Ts, A0, omega, filename)
%
% Inputs:
%   t        - time vector from ODE solver (e.g., from ode45)
%   x        - state matrix [q(t), dq(t)]
%   Ts       - sampling period (in seconds)
%   A0       - input amplitude for u(t) = A0 * sin(omega * t)
%   omega    - input frequency (in rad/s)
%   filename - output CSV filename

    % Time vector for resampling
    t_sampled = t(1):Ts:t(end);

    % Resample q and dq using interpolation
    q_sampled  = interp1(t, x(:,1), t_sampled);
    dq_sampled = interp1(t, x(:,2), t_sampled);

    % Estimate second derivative using central finite differences
    ddq_sampled = zeros(size(q_sampled));
    N = length(q_sampled);

    for k = 2:N-1
        ddq_sampled(k) = (q_sampled(k+1) - 2*q_sampled(k) + q_sampled(k-1)) / Ts^2;
    end

    % Evaluate input u(t)
    u_sampled = A0 * sin(omega * t_sampled);

    % Create table and export to CSV
    T = table(t_sampled', q_sampled', dq_sampled', ddq_sampled', u_sampled', ...
        'VariableNames', {'t', 'q', 'dq', 'ddq', 'u'});

    writetable(T, filename);
    fprintf('Sampling data saved to file: %s\n', filename);
end