From value d and b, new values A and B are computed shown in Fig. 11.12. It is required to store A and B after calculation. We can use the same memory locations to store A − B where a − b were stored. The two memory locations for each are required because A, B or a, b each are complex numbers. Hence, four memory locations are required, i.e., two for d or A and two for b or B for one butterfly computation.
Memory locations for one butterfly = 2 = 2 = 4 (11.131)
where A is stored in place of d and B is stored in place of ‘b’. This is known as in place computation which reduces memory requirement. This is the main advantage.
From Fig. 11.12 for N = 8, the computations are performed stage ...