Table 3.

Comparison of run times (in seconds) for a PET imaging problem on the simulated data in (30). The image has p = 64 × 64 = 4, 096 pixels and is interrogated by d = 2, 016 detectors. The columns labeled Function refer to the converged value of the objective function. The results under the heading QN(10) on CPU invoke quasi-Newton acceleration (42) with 10 secant conditions.

Penalty μ	CPU			GPU				QN(10) on CPU
	Iters	Time	Function	Iters	Time	Function	Speedup	Iters	Time	Function	Speedup
0	100000	14790	−7337.152765	100000	282	−7337.153387	52	6549	2094	−7320.100952	n/a
10−7	24457	3682	−8500.083033	24457	70	−8508.112249	53	251	83	−8500.077057	44
10−6	6294	919	−15432.45496	6294	18	−15432.45586	51	80	29	−15432.45366	32
10−5	589	86	−55767.32966	589	2	−55767.32970	43	19	9	−55767.32731	10