function Z = add_hill(Z,NX,NY,i1,j1,r,h)

for i = 1:NX
    for j = 1:NY
        distanceX = mod(i-i1+NX/2,NX)-NX/2;
        distanceY = mod(j-j1+NY/2,NY)-NY/2;
        totalDistance = sqrt(distanceX^2+distanceY^2);
        if (totaDistance<r)
            Z(distanceX,disatnceY) = Z(distanceX,distanceY) + h*(cos(totalDistance/r*pi/2))^2;
        end
    end
end