Difference between revisions of "Distributed Simulated Annealing"
Line 29: | Line 29: | ||
== Performance Graphs == | == Performance Graphs == | ||
− | For the purposes of benchmarking, we present results for 4 different problems: Northern California (Well Constrained), Northern California (Poorly Constrained), All California (Well Constrained), and All California (Poorly Constrained). These 4 problems help demonstrate the affect of problem size and degree of constraints on the parallel speedup of the parallel SA algorithm. | + | For the purposes of benchmarking, we present results for 4 different problems: Northern California (Well Constrained), Northern California (Poorly Constrained), All California (Well Constrained), and All California (Poorly Constrained). These 4 problems help demonstrate the affect of problem size and degree of constraints on the parallel speedup of the parallel SA algorithm. Due to the random nature of simulated annealing, we did 5 identical runs with each parameterisation and averaged the results. |
{| border="1" | {| border="1" | ||
!Dataset | !Dataset | ||
− | !Northern California (Well Constrained) | + | !Northern California (Well Constrained)<br>35,554 elements |
− | !Northern California (Poorly Constrained) | + | !Northern California (Poorly Constrained)<br>35,554 elements |
− | !All California (Well Constrained) | + | !All California (Well Constrained)<br>130,786 elements |
− | !All California (Poorly Constrained) | + | !All California (Poorly Constrained)<br>130,786 elements |
|- | |- | ||
!Energy vs Time | !Energy vs Time | ||
Line 76: | Line 76: | ||
== Conclusions == | == Conclusions == | ||
− | The parallel simulated annealing algorithm clearly improves upon the classical serial approach. | + | The parallel simulated annealing algorithm clearly improves upon the classical serial approach. For smaller, well constrained problems, we saw a maximum speedup (averaged over 5 identical runs) of over 20x for a 50 node run (4 threads per node, 200 threads total). For less constrained, and/or larger solution spaces, we saw more marginal (6x-15x) improvement. Although |
Revision as of 23:12, 6 September 2011
Contents
Introduction
An inversion-based methodology is being developed for the 3rd Uniform California Earthquake Rupture Forecast (UCERF3) that simultaneously satisfies available slip-rate, paleoseismic event-rate, and magnitude-distribution constraints. Simulated Annealing (Kirkpatrick 1983) is a well defined method for solving optomization problems, but can be slow for problems with a large solution space, such as the UCERF3 "Grand Inversion." We present a parallel simulated annealing approach to solve for the rates of all ruptures that extend through the seismogenic thickness on major mapped faults in California.
Serial SA Algorithm
- s = s0; e = E(s)
- sbest = s; ebest = e
- k = 0
- while k < max_iterations:
- snew = neighbour(s)
- enew = E(snew)
- if P(e, enew, temperature) > random(); then
- s = snew; e = enew
- if enew < ebest
- sbest = snew; ebest = enew
- k++'
Parallel SA Algorithm
- s = s0; e = E(s)
- sbest = s; ebest = e
- k = 0
- while k < max_iterations
- on n processors, do nSubIterations iterations of serial SA
- find processor with best overall (lowest energy) solution, sbest
- redistribute sbest, ebest to all processors
- k += nSubIterations
Implementation
We implemented the parallel simulated annealing algorithm in OpenSHA (http://www.opensha.org), a Java-based framework for Seismic Hazard Analysis which is being used to develop UCERF3. All benchmarking calculations presented here were calculated on the USC HPCC cluster (http://www.usc.edu/hpcc/). There are two levels of parallelization used: cluster lever, and node level. Each HPCC node has 8 processors, so threading is used to make use of all available processors. We determined that 4 threads/node was optimal, possibly due to the use of a parallel sparse matrix multiplication package (used to calculate misfit, and thus energy) becoming overloaded when used with 8 threads/node. For cluster level parallelization, we used MPJ Express (http://mpj-express.org/, Baker 2007), a Java-based MPI implementation.
Performance Graphs
For the purposes of benchmarking, we present results for 4 different problems: Northern California (Well Constrained), Northern California (Poorly Constrained), All California (Well Constrained), and All California (Poorly Constrained). These 4 problems help demonstrate the affect of problem size and degree of constraints on the parallel speedup of the parallel SA algorithm. Due to the random nature of simulated annealing, we did 5 identical runs with each parameterisation and averaged the results.
Conclusions
The parallel simulated annealing algorithm clearly improves upon the classical serial approach. For smaller, well constrained problems, we saw a maximum speedup (averaged over 5 identical runs) of over 20x for a 50 node run (4 threads per node, 200 threads total). For less constrained, and/or larger solution spaces, we saw more marginal (6x-15x) improvement. Although