1. Random Number Testing and RDM
Random numbers are particularly important for the Radioactive Decay Module
Sampling decay times is important for a number of use cases:
nuclear physics: e.g. looking for rare processes, summing effects
Medical physics: very large data sets (current application has 500MBq and simulated for 10's of seconds) → critical is the background (scattering, energy pile-up) and random contribution (events overlapping)
Repetition and more significantly granularity are crucial
Computation time also has an impact – the RDM can be quite heavy (e.g. beta decay) so the efficiency of the random number generation is correlated
RDM mini-workshop
22nd March 2016

2. Random Number Testing Create random numbers in a flat distribution:
Unit test: RNG.flat()
Unit test: G4UniformRand()
G4UniformRand() inside an application
Time distribution of decay window biased particles from RDM
Outputs:
Measure time for trials
Determine time interval between events (granularity)
Record created times (1s interval)
Sort in increasing times
Plot the distribution of time intervals between events (necessary requirement for random event pile-up studies)
PRNGs tested:
Ranecu
Ranlux
Ranshi
Ranlux64
Mersenne Twist
MixMax
Geant ref02
RDM mini-workshop
22nd March 2016

3. Times from Trial Test (laptop/ubuntu)
Generator
Sequential
flat() /s
G4UniformRand()
Multithreaded
Ranecu
11.68
15.19
9.68
15.04
Ranlux
130.62
142.55
95.18
115.59
Ranshi
8.71
7.13
7.4
12.71
Ranlux64
114.58
116.81
128.29
147.53
MTwist
6.91
32.23
21.27
10.79
MixMax
10.26
11.3
7.56
15.09
RDM mini-workshop
22nd March 2016

4. Times from Trial Test (cluster/RHEL)
Generator
Sequential
flat() /s
G4UniformRand()
Multithreaded
Ranecu
10.51
13.56
10.82
18.08
Ranlux
70.79
76.27
73.82
88.58
Ranshi
5.39
7.98
5.64
11.36
Ranlux64
83.2
88.1
91.01
96.14
MTwist
6.94
10.24
8.0
11.3
MixMax
8.66
12.6
10.56
13.88
RDM mini-workshop
22nd March 2016

5. Application Test
Create positrons with a uniform (flat) timing distribution – across 1s
Sequential
RDM mini-workshop
22nd March 2016

6. ST: 100k G4UniformRand() - Ranecu
RDM mini-workshop
22nd March 2016

7. ST: 100k G4UniformRand() - Ranlux
RDM mini-workshop
22nd March 2016

8. ST: 100k G4UniformRand() - Ranshi
RDM mini-workshop
22nd March 2016

9. ST: 100k G4UniformRand() - Ranlux64
RDM mini-workshop
22nd March 2016

10. ST: 100k G4UniformRand() - MTwist
RDM mini-workshop
22nd March 2016

11. ST: 100k G4UniformRand() - MixMax
RDM mini-workshop
22nd March 2016

12. Application Test
Create positrons with a uniform (flat) timing distribution – across 1s
Multi threaded (4 threads)
RDM mini-workshop
22nd March 2016

13. MT: 100k G4UniformRand() - Ranecu
RDM mini-workshop
22nd March 2016

14. MT: 100k G4UniformRand() - Ranlux
RDM mini-workshop
22nd March 2016

15. MT: 100k G4UniformRand() - Ranshi
RDM mini-workshop
22nd March 2016

16. MT: What's happened to Ranshi
The time is somehow limited to ~ (signed 32-bit) – bit loss?
RDM mini-workshop
22nd March 2016

17. MT: 100k G4UniformRand() - Ranlux64
RDM mini-workshop
22nd March 2016

18. MT: 100k G4UniformRand() - MTwist
RDM mini-workshop
22nd March 2016

19. MT: 100k G4UniformRand() - MixMax
Super slow – race condition?
RDM mini-workshop
22nd March 2016

20. Profiling?
Gprof and kcachegrind both seem to indicate minimal impact/differences between mixmax and ranecu
Threadlock hazard blocking mixmax?
RDM mini-workshop
22nd March 2016

21. Application Test
Create positrons with a uniform (flat) timing distribution – across 1s
Multi threaded, but with only ONE thread
RDM mini-workshop
22nd March 2016

22. MT1: 100k G4UniformRand() - Ranecu
RDM mini-workshop
22nd March 2016

23. MT1: 100k G4UniformRand() - Ranlux
RDM mini-workshop
22nd March 2016

24. MT1: 100k G4UniformRand() - Ranshi
RDM mini-workshop
22nd March 2016

25. MT1: What's happened to Ranshi?
The time is somehow limited to ~ (signed 32-bit) – bit loss?
RDM mini-workshop
22nd March 2016

26. MT1: 100k G4UniformRand() - Ranlux64
RDM mini-workshop
22nd March 2016

27. MT1: 100k G4UniformRand() - MTwist
RDM mini-workshop
22nd March 2016

28. MT1: 100k G4UniformRand() - MixMax
Super slow – race condition?
RDM mini-workshop
22nd March 2016

29. Radioactive Decay Time Window
Set decay time window to 1s
Record the decay time of 22Na
RDM should use G4UniformRand() across the time window and weighted by the half-life
Essentially flat for 22Na (>2 year half-life)
RDM mini-workshop
22nd March 2016

30. RDM Test
Sequential
RDM mini-workshop
22nd March 2016

31. ST: 100k RDM (22Na decay) - Ranecu
RDM mini-workshop
22nd March 2016

32. ST: 100k RDM (22Na decay) - Ranlux
RDM mini-workshop
22nd March 2016

33. ST: 100k RDM (22Na decay) - Ranshi
RDM mini-workshop
22nd March 2016

34. ST: 100k RDM (22Na decay) - Ranlux64
RDM mini-workshop
22nd March 2016

35. ST: 100k RDM (22Na decay) - MTwist
RDM mini-workshop
22nd March 2016

36. ST: 100k RDM (22Na decay) - MixMax
RDM mini-workshop
22nd March 2016

37. RDM Test
Multi Threaded
RDM mini-workshop
22nd March 2016

38. MT: 100k RDM (22Na decay) - Ranecu
RDM mini-workshop
22nd March 2016

39. MT: 100k RDM (22Na decay) - Ranlux
RDM mini-workshop
22nd March 2016

40. MT: 100k RDM (22Na decay) - Ranshi
RDM mini-workshop
22nd March 2016

41. MT: 100k RDM (22Na decay) - Ranlux64
RDM mini-workshop
22nd March 2016

42. MT: 100k RDM (22Na decay) - MTwist
RDM mini-workshop
22nd March 2016

43. MT: 100k RDM (22Na decay) - MixMax
RDM mini-workshop
22nd March 2016

44. RDM Test Multi Threaded, but with only ONE thread RDM mini-workshop
22nd March 2016

45. MT: 100k RDM (22Na decay) - Ranlux64
RDM mini-workshop
22nd March 2016

46. MT1: 100k RDM (22Na decay) - Ranlux64
RDM mini-workshop
22nd March 2016

47. Times from RDM (laptop/ubuntu)
Generator
Sequential
positron /s
22Na
Multithreaded
1 Multithreaded
Ranecu
27.8
34.5
48.4
(69.7s)
[gprof: 5m17]
32.9
Ranlux
31.1
58.0
37.5
(93.3s)
[gprof: 7m10)
38.6
Ranshi
30.7
51.1
18.9
(29.65s)
[gprof: 42.7s]
11.8
Ranlux64
31.6
60.1
44.4
(114.6s)
[gprof: 7m2s]
55.5
MTwist
26.4
56.5
37.3
(75.7s)
[gprof: 7m22s]
30.6
MixMax
28.6
46.2
17m12.3
(62m28.5s)
[gprof: 945m28s]
31m57
MT: 22Na similar behaviour, except MixMax – real 43m, user: 54m
RDM mini-workshop
22nd March 2016

48. Times from RDM (cluster/RHEL)
Generator
Sequential
positron /s
Single Threaded
22Na
Multithreaded
1 Multithreaded
Ranecu
46.1
2m34.3
(4m38s)
44.6
Ranlux
40.4
2m26.6
(4m43s)
49.0
Ranshi
40.2
2m21.7
(3m44s)
16.7
Ranlux64
43.2
2m28.5
(4m39s)
49.2
MTwist
38.7
2m27.2
(4m35s)
42.3
MixMax
40.0
3m25.1
(45m11s)!!!
27m30.4
RDM mini-workshop
22nd March 2016

49. RDM Biasing Options
For PET: A common use case is to have an activity (Bq) and not be interested in decay time
GATE “recommends” modifying the PDG lifetime
This (previous external) hack now requires modifying Geant4 source
The RDM biasing fixes this, however, needs work – default is flat-branching ratios (feature) and daughters are not decayed (bug)
RDM mini-workshop
22nd March 2016

50. GATE “fix”
RDM mini-workshop
22nd March 2016

51. RDM mini-workshop
22nd March 2016

52. Summary
The issues with random numbers and MT and RDM are still present – no surprise we didn't change anything....
With new PRNGs (mixmax) there seem to be other problems with race conditions
More investigation needed
Biasing options could be more user friendly (as previously self-proposed)
RDM mini-workshop
22nd March 2016