Matlab FFT Code

close all;
    clear all;
    clc;
    ct = 1;
    for i = 0.030:.00400000000000000000:0.150
        format = '%#0.3f\n';
        str = num2str(i, format);
        modstr = str(2:end);
        ez = h5read(sprintf('hsli%s.h5',modstr),'/ez');
        N = length(ez);
        res = 5; % Samples per unit length
        dx = 1/res; % Length increment per sample
        x = (0:N-1) * dx; % Position vector
        NFFT = 2^nextpow2(N); % Next power of 2 from length of y
        Y = fft(ez,NFFT) / (N * max(ez));
        kfft = res / 2 * linspace(0, 1, NFFT / 2 + 1);
        ABSY = 2 * abs(Y(1:NFFT / 2 + 1));
    %     plot(kfft, ABSY);
        title('Amplitute Spectrum', 'fontweight', 'bold');
        xlabel('Wavevector(k)', 'fontweight', 'bold');
        ylabel('|Y(f)|', 'fontweight', 'bold');
        ind(ct,1) = find(ABSY == max(ABSY));
        k(ct,1) = kfft(ind(ct,1));
        w(ct,1) = i;
        ct = ct + 1;
    end
    plot(w, k * 2 * pi, '-r', 'linewidth', 3);
    title('Dispersion Graph', 'fontweight', 'bold');
    xlabel('Wavevector(k)', 'fontweight', 'bold');
    ylabel('Angular Frequency(w)', 'fontweight', 'bold');