_speed_array = 1450:5:1550;
for index = 1:length(sound_speed_array)
    
    <span class="comment">% update value of sound speed</span>
    medium.sound_speed = sound_speed_array(index);
    
    <span class="comment">% run the reconstruction</span>
    p0_recon = kspaceFirstOrder2D(kgrid, medium, source, sensor, input_args{:});
    
    <span class="comment">% update the value of the focus function</span>
    focus_func(1, index) = sharpness(p0_recon, 'Brenner');
    focus_func(2, index) = sharpness(p0_rec