SUB displacements(x(),y(),Lx,Ly,R2cum(),norm(),ndata,ndiff)
    DECLARE DEF separation        ! function same as in Program md
    FOR idiff = 1 to ndiff
        FOR i = 1 to ndata - idiff
            LET dx = separation(x(i+idiff) - x(i),Lx)
            LET dy = separation(y(i+idiff) - y(i),Lx)
            LET R2cum(idiff) = R2cum(idiff) + dx*dx + dy*dy
            LET norm(idiff) = norm(idiff) + 1
        NEXT i
    NEXT idiff
END SUB