So far we've looked only at "perfect crystals." The remaining presets address several issues concerning imperfect crystals.
Here is a perfect "diatomic crystal" with equally spaced atoms of equal size but different atomic number (electronic charge). From the ratio of the intensities of the strong to weak lines of 4/1 you should be able to conclude that the ratio of atomic numbers of the two crystals is 3/1.
"laue" can mix up the crystal, putting one kind of atom where the other kind is supposed to be and vice versa. The order parameter p describes the amount of mixing. (p=1 is the ordered crystal; p=0 gives a random assignment of atoms to sites.)
Calculate for three different values of p: 0, 1, and 0.5, and copy diffraction for each of these. (It's probably easier to compare if they're separate: you could try steal data to put them on a single plot.) There are three features to note: