For implementations with less high demands on the throughput, it is
possible to project to a configuration with a smaller number of butterfly PEs.
Horizontal projection leads to N/2 PEs with a decrease in throughput by a
factor of long2N comparison to a 2-D array. Vertical projection yields log2N
PEs and a decrease in throughput by a factor of N/2. A single butterfly PE
must sequentially carry out the processing (N/2) log2 N times. The essential
data are summarized in Table 7.3.2.