Whats the purpose of cos function?

%build the matrix
n = 0:N-1;

for k = 0:N-1

     if (k>0)
        C(k+1,n+1) = cos(pi*(2*n+1)*k/2/N)/sqrt(N)*sqrt(2);
     else
        C(k+1,n+1) = cos(pi*(2*n+1)*k/2/N)/sqrt(N);
     end   
  end

Is that because of using dct ?or cos function have any other functions ?

Answer 1

[Walter Roberson]

The cosine function was originally created as a "make work" project for medieval tutors, to convince patrons that the tutors knew something exotic that was worth paying for; in this, the trig functions replaced the earlier Latin Squares Mysteries Strategic Work Initiative.

Later, cosine functions were found to have some useful mathematical properties.