. Author manuscript; available in PMC: 2016 May 1.

Published in final edited form as: J Struct Biol. 2015 Mar 31;190(2):200–214. doi: 10.1016/j.jsb.2015.03.009

Table 3.

CPU time and speedup for real data experiments. Times are reported as the sum of execution time across all processes.

	Average SSD^a Time (min)	Average Iteration Time (min)	# EM Iterations	Total CPU Time (hrs)
25K Images, 5° Sampling
StandardEM	23950	23956	5	1996
SubspaceEM-1x	15.9	18.8	8	2.6
SubspaceEM-2x	19.2	21.8	7	2.7
SubspaceEM-Overall	17.5	20.2	15	5.3
Speedup^b	1369	1186	-	377

SSD = Sum of squared differences. In StandardEM, the differences are calculated between images and projections. In SubspaceEM, the differences are between approximated images and approximated projections.

Speedup is calculated as (StandardEM time)/(SubspaceEM-Overall time).