CPU-time & $N$

Figure 4 compares computational times for both the NDFT and the NFFT, see ./example/timing.

Figure: The elapsed CPU-time with respect to $N$ for Kaiser Bessel window, parameters $m=6,\, \sigma=2,\, M=N$; left, $d=1$: NDFT (circle), NFFT (no precomputation, x), NFFT (simple interface, $+$), NFFT (maximum precomputation, triangle); middle, $d=2$: NDFT (circle), NFFT (simple interface, $+$); right, $d=3$: NDFT (circle), NFFT (simple interface, $+$).

Figure 5 compares computational times for single steps of the NFFT, see ./example/timing.

Figure: The elapsed CPU-time with respect to $N$ for Kaiser Bessel window, parameters $d=2,\,m=6,\, \sigma\ge2,\, M=N$; from left to right: multiplication with ${D}$, ${F}$, and ${B}$ respectively; no precomputation (x), simple interface ($+$), and maximum precomputation (triangle).