When one positive and one negative contribution cancel exactly, the structure factor drops to zero and the peak disappears, producing a systematic absence. The summed amplitude F = 1 + (-1) = 0 gives intensity 0 squared = 0 exactly for the stated toy cancellation ledger; real diffraction has partial cancellation, lattice disorder, background, finite resolution, and detector response uncertainty.
A missing training peak can come from exact cancellation in the signed sum. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Opposite signs can cancel
One positive and one negative contribution give amplitude 0.
F=1+(−1)=0
A zero sum gives a missing peak
The intensity is exactly 0. This explains cancellation, not empirical diffraction corrections.