Identication and Estimation of Nonsymmetric Determinantal Point Processes
Organizations: University of Toronto, Toulouse School of Economics and CREST · Department of Mathematics and Statistics, Concordia University, Montreal, Canada
Abstract
Determinantal point processes (DPPs) provide tractable distributions for nite random sets, but the usual symmetric-kernel specication imposes nonpositive pairwise dependence. Statistical research on nonsymmetric DPPs, which can accommodate positive dependence, remains limited. We study identication and estimation for this class. First, we establish the equivalence of two sucient conditions for a nonsymmetric kernel to dene a valid DPP. Second, we develop the identication theory for nonsymmetric DPPs. Third, we develop cardinality-truncated maximum-likelihood estimation and estimation by averaged stochastic gradient descent. Under suitable identication and regularity conditions, we establish consistency and asymptotic normality for both estimators. Simulations examine identication, the eects of truncation, and the nite-sample performance of the estimators. We illustrate the methods with two cyber applications at markedly dierent sampling frequencies: weekly sector-by-breach data and second-by-second enterprise authentication data with more than ve million set observations.
Figures & tables
| Mean | Median | size | size | ||
|---|---|---|---|---|---|
| 500 | 306.9 | 0.327 | 0.753 | 0.050 | 0.007 |
| 2000 | 1226.9 | 0.172 | 0.390 | 0.051 | 0.004 |
| 8000 | 4906.5 | 0.079 | 0.126 | 0.054 | 0.007 |
| Design | |||||
|---|---|---|---|---|---|
| Baseline | |||||
| Dense | |||||
| Weak |
| Design | Mean | RMSE | Trace efficiency | Regular share | Score size at | |
|---|---|---|---|---|---|---|
| Baseline | 4 | 3730.0 | 0.180 | 0.745 | 0.985 | 0.060 |
| 5 | 3945.5 | 0.159 | 0.902 | 0.989 | 0.058 | |
| 8 | 4000.0 | 0.150 | 1.000 | 0.993 | 0.058 | |
| Dense | 4 | 1976.0 | 0.216 | 0.417 | 0.959 | 0.044 |
| 5 | 3037.9 | 0.163 | 0.690 | 0.988 | 0.045 | |
| 8 | 4000.0 | 0.133 | 1.000 | 0.997 | 0.040 |
| Mean | Size of | Size of | |
|---|---|---|---|
| 4 | 1975.2 | 0.044 | 0.267 |
| 5 | 3037.5 | 0.045 | 0.107 |
| 8 | 4000.0 | 0.040 | 0.040 |
| Design | Mean | MLE RMSE | ASGD RMSE | ASGD/MLE | |
|---|---|---|---|---|---|
| Baseline | 4 | 238717 | 0.0221 | 0.2152 | 9.75 |
| 5 | 252499 | 0.0200 | 0.2222 | 11.10 | |
| 8 | 256000 | 0.0186 | 0.2712 | 14.60 | |
| Dense | 4 | 126386 | 0.0231 | 0.4725 | 20.42 |
| 5 | 194360 | 0.0185 | 0.2546 | 13.75 | |
| 8 | 256000 | 0.0158 | 0.5522 | 34.87 |
| Specification | Dependence parameters | Log likelihood | AIC | BIC | Maximum absolute score |
|---|---|---|---|---|---|
| Time-adjusted independence | 0 | -6710.677 | 0.0 | 0.0 | – |
| Symmetric Kronecker DPP | 16 | -6710.677 | 32.0 | 106.4 | |
| Axis | 16 | -6660.681 | -68.0 | 6.4 | |
| Sector-led | 22 | -6637.049 | -103.3 | -1.0 | |
| Breach-led | 26 | -6619.405 | -130.5 | -9.7 | |
| Two-way | 32 | -6609.976 | -137.4 | 11.4 |
| Rank | Pair | Correlation | Pair type |
|---|---|---|---|
| 1 | MED–HACK and MED–DISC | 0.44799 | Breach type |
| 2 | BUS–HACK and MED–DISC | 0.29953 | Cross |
| 3 | BUS–HACK and MED–HACK | 0.29064 | Sector |
| 4 | BUS–HACK and MED–ELET | 0.29055 | Cross |
| 5 | EDU–ELET and PUBLIC–ELET | 0.28169 | Sector |
| Pair class | Pairs | Mean | Mean | Largest |
|---|---|---|---|---|
| Same sector, different breach types | 30 | 0.0151 | 0.0158 | MED–DISC / MED–INSD (0.0354) |
| Different sectors, same breach type | 40 | 0.0285 | 0.0300 | BUS–ELET / MED–ELET (0.0733) |
| Different sectors, different breach types | 120 | 0.0114 | 0.0136 | BSF–INSD / EDU–HACK (0.0555) |
| Initial value | Initial | Raw endpoint | Averaged | ||
|---|---|---|---|---|---|
| Axis warm start | -6660.681 | -6919.064 | -6748.920 | 129.515 | 0.0777 |
| Cellwise start | -6708.017 | -6931.639 | -6770.810 | 151.405 | 0.0559 |
| Panel A: how the data days are used | |
|---|---|
| Data days | Use |
| 1 | Select 20 high-activity candidate source computers |
| 2–8 | Choose the ten-computer panel; set starting values and coordinate scales |
| 9–15 | Not used for panel selection, tuning, or main estimation |
| 16–19 | Run candidate ASGD settings |
| 20–22 | Evaluate candidate estimates with coefficients held fixed |
Appendix figures & tables3 assets
Supplementary material from the paper’s appendix.
Appendix
| Design | |||
|---|---|---|---|
| Panel A: normalized Fisher-risk ratio | |||
| Baseline | 4 | ||
| 5 | |||
| 8 | |||
| Dense | 4 | ||
| 5 | |||
| Panel A: estimator accuracy | |||||
|---|---|---|---|---|---|
| Design | MLE RMSE | ASGD RMSE | RMSE ratio | Risk ratio | |
| Static | 64,000 | 0.02369 | 0.07828 | 3.30 | 4.12 |
| 256,000 | 0.01255 | 0.02569 | 2.05 | 2.02 | |
| 1,000,000 | 0.00706 | 0.01006 | 1.43 | 1.39 | |
| Contextual | 64,000 | 0.02450 | 0.07283 | 2.97 | 4.08 |
| 256,000 | 0.01216 | 0.02544 | 2.09 | 2.14 | |
| \widehat{S}=\begin{array}[]{c|rrrrr}&\mathrm{BSF}&\mathrm{BUS}&\mathrm{MED}&\mathrm{EDU}&\mathrm{PUBLIC}\\ \hline\cr\mathrm{BSF}&0&1.433&1.168&1.073&0.924\\ \mathrm{BUS}&-1.433&0&1.978&-1.603&-1.537\\ \mathrm{MED}&-1.168&-1.978&0&1.344&-0.631\\ \mathrm{EDU}&-1.073&1.603&-1.344&0&2.068\\ \mathrm{PUBLIC}&-0.924&1.537&0.631&-2.068&0\end{array} |
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