Error in Kramers-Kronig Relations

I am trying to convert extinction coefficient to refractive index.

Unrecognized function or variable 'k_vec'.

Error in KramersKroigRelations (line 12)

n_vec = zeros(size(k_vec));

I tried to set up k_vec to indicate the refractive indices.

k_vec to refractive indices

clear 
% read data from textinctionSpectrum.txt
data = readtable('extinctionSpectrum.txt');
wavelength = data{:,1}; % wavelength in nm
extinction = data{:,2}; % extinction coefficient
% w = 2*pi*3e17./wavelength;
% convert extinction coefficient to refractive index
n_vec = zeros(size(k_vec));
for i = 1:length(k_vec)
    k = k_vec(i);
    n_real = 1 + (2/pi)*integral(@(w_prime) w_prime.*k./(w_prime.^2 - w.^2), 0, Inf, 'PrincipalValue', true);
    n_imag = (2/pi)*integral(@(w_prime) w.*k./(w_prime.*(w_prime.^2 - w.^2)), 0, Inf, 'PrincipalValue', true);
    n_vec(i) = n_real + 1i*n_imag;
end
figure;
plot(w, real(n_real), 'b-', w, imag(n_imag), 'r-');
xlabel('Wavelength (nm)');
ylabel('Refractive index');
legend('Real part', 'Imaginary part');

Answer 1

[the cyclist]

You haven't defined a variable named k_vec before this line of code

n_vec = zeros(size(k_vec));

so MATLAB errors out when it tries to get the size of it.