function [Energy, Waist, Penalty] = fitness( q_0, q_final, x_final, optics_positions, optics_focal_length, lambda )
%Outputs fitness of suggested solution
    x0 = 0;
    Np=20; % # of pts between start position and second lens
    N_collimated = 10; % # of pts between second lens and third lens to be collimated region
    
    x1=optics_positions(1);
    x2=optics_positions(2);
    x3=optics_positions(3);
    
    x_array1=linspace(x0,x2,Np);
    x_array2=linspace(x2, x3, N_collimated);
    x = cat(2,x_array1,x_array2);
    
    q_f_trial_forward = gbeam_propagation(x,q_0,x0,optics_placer(optics_positions, optics_focal_length));
    [Waist_trial_forward, Radius_trial_forward] = q2wr(q_f_trial_forward, lambda);
    q_f_trial_backward = gbeam_propagation(x,q_final,x_final,optics_placer(optics_positions, optics_focal_length));
    [Waist_trial_backward, Radius_trial_backward] = q2wr(q_f_trial_backward, lambda);

    Energy = 0;
    Penalty_waist_mismatch = sum(abs((Waist_trial_forward-Waist_trial_backward)./min(Waist_trial_forward, Waist_trial_backward)))/Np;
    
    Energy = 1e-2*Penalty_waist_mismatch;
    
    % penalty calculation
    % do not put lenses too close to each other and end positions
    lens_size=0.03;
    

    
    d(1)=abs(x1-x2);
    d(2)=abs(x2-x3);
    d(3)=abs(x1-x3);
    
    d_from_start=abs(x0-optics_positions);
    d_from_end=abs(x_final-optics_positions);
    
    
    
    d=cat(2, d, d_from_start, d_from_end);
    
    coef = 1;
   
    penalty_lenses_too_closely_spaced =coef*sum( exp(-(d/(lens_size)).^12) );
    
    Energy = Energy + penalty_lenses_too_closely_spaced;
    
    % make sure that lenses are between ends
    d_from_start=(x0-optics_positions);
    d_from_end=(optics_positions-x_final);
    
    d = cat(2, d_from_start, d_from_end);
    
    coef = 1e-2;
    distance_scaling=100;
    penalty_lenses_outside_optical_path = coef * sum(1 + tanh(distance_scaling*d));
    
    Energy = Energy + penalty_lenses_outside_optical_path;
    
    % make collimated region between 2nd and 3rd lens   
    %intialize intermediate points between lenses
    q_intermediate = q_f_trial_forward((x2<x) & (x<x3));
    lambda_over_waist_sq = (-imag(1./q_intermediate)); %with numerical factor
    
    coef = 1e-3;
    penalty_not_collimated_beam = coef * sum(exp((std(lambda_over_waist_sq)/mean(lambda_over_waist_sq)/abs(optics_positions(2) - optics_positions(3)))));
    Energy = Energy + penalty_not_collimated_beam;
    
    Penalty = [ penalty_lenses_too_closely_spaced; penalty_lenses_too_closely_spaced; penalty_not_collimated_beam];
end