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Markov Equivalence and Consistency in Differentiable Structure Learning
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Shows that differentiable acyclicity-constrained likelihood scores with quasi-MCP regularization recover the sparsest DAG and, under faithfulness, the Markov equivalence class, and are scale-invariant for Gaussian models.
Problem
Continuous (differentiable) score-based DAG structure learning relies on strong identifiability assumptions and uses least squares loss, which is sensitive to data scale (varsortability); it is unclear which score guarantees recovery of the sparsest model or Markov equivalence class under nonidentif
Approach
Replace the least squares score with the negative log-likelihood regularized by a differentiable nonconvex quasi-MCP penalty (an approximation of the l0 penalty) under an acyclicity constraint; show global minimizers are minimal-edge I-maps (sparsest representations), hence in the Markov equivalence class under faithfulness, and that the Gaussian log-likelihood score is scale-invariant.
Key results
- Global minimizers of log-likelihood plus quasi-MCP (for small lambda, delta) recover the minimal-edge equivalence class, and under faithfulness the Markov equivalence class (Theorems 3.x and 4.x).
- Gaussian log-likelihood score is scale-invariant: standardizing data does not change the recovered DAG structure at global optima, while NOTEARS, GOLEM and DAGMA degrade sharply on standardized data.
- On small graphs (ER-2, p=10) the logll-notears variants stay robust under standardization alongside PC and FGES, while VarSort and other CSL baselines deteriorate.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Replace least squares with log-likelihood plus MCP | NOTEARS · Different graph types | SHD | Helped |
| Replace least squares with log-likelihood plus MCP | NOTEARS · Sparse graphs {ER1, SF1} | SHD | Mixed |
| Standardize the input data | GOLEM · Simulated graph data | SHD | Hurt |
| Standardize the input data | NOTEARS · Simulated graph data | SHD | Hurt |
| Standardize the input data | DAGMA · Simulated graph data | SHD | Hurt |
| Standardize the input data | logll-notears-sample · Simulated graph data | SHD | Mixed |
| Standardize the input data | logll-notears-population · Simulated graph data | SHD | Mixed |
| Standardize the input data | logll-notears-sample · ER-2, 10 nodes | SHD | No clear effect |
| Standardize the input data | logll-notears-population · ER-2, 10 nodes | SHD | No clear effect |
| Standardize the input data | logll-notears-sample · ER-2, 50 nodes | SHD | Hurt |
| Standardize the input data | logll-notears-population · ER-2, 50 nodes | SHD | Hurt |
| Use MCP or SCAD instead of quasi-MCP (ablation) | Regularized log-likelihood structure learning · Gaussian DAG models | Recovery of minimal equivalence class | No clear effect |
Surprising findings
- Standardization substantially degrades GOLEM, NOTEARS and DAGMA to roughly empty-graph performance, and VarSort with standardized data exceeds SHD 300 on average.
Limitations
- Theory relies on finite equivalence class, Lipschitz B(psi), and bounded level-set assumptions for general models.
- Global optimization becomes difficult as graph size grows, so scale invariance is not fully realized empirically for p=50 and above.
- Only parametric models and observational data are considered; interventional data and nonparametric models are left to future work.
Experimental setup
Datasets: synthetic linear Gaussian DAGs (ER and SF graphs)
Benchmarks: synthetic ER and SF graphs with p=10,20,50,70,100
Metrics: structural Hamming distance between CPDAGs
Baselines: NOTEARS GOLEM DAGMA VarSort FGES PC
Builds on: NOTEARS MCP SCAD sparsest Markov representation
Closest papers by meaning
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- A Fixed-Parameter Tractable Algorithm for Counting Markov Equivalence Classes with the Same Skeleton (AAAI 2024 · similarity 0.87)
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