function Y = transform(X,trans_type)
% input transformations
% choose transformation type
% 1 - linear, no transformation
% 2 - add quadratic terms
% 3 - logarithmic terms (x,y, log x, log y)
% 4 - frequency transformation

switch trans_type
case 1
   Y = X;
case 2
   Y = [X X.^2];
case 3
   Y = [X exp(abs(X))];
case 4
   freq_range = kron(X,[1 2 4 8 16]);
   Y = [sin(freq_range) cos(freq_range)];
otherwise
   error('No such transformation type');
end
