REVIEW 4 major objections 5 minor 1 cited by
Learning Aggregation Rules in Participatory Budgeting: A Data-Driven Approach
T0 review · 4 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read The paper shows that a neural network can learn participatory budgeting aggregation rules from example votes and outcomes, reproducing standard rules and recovering Proportional Approval Voting as a 30/70 compromise between welfare and…
desk verdict A genuinely useful extension of Set Transformer learning to participatory budgeting, with a PAV-resemblance claim that overstates what average ratios can support. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing component is the ST+PMA architecture: a Set Transformer in which a pooling-by-multihead-attention (PMA) layer is moved from the decoder to before the encoder, compressing the voter-by-project approval matrix into a project-dimensional latent space so that the number of voters no longer affects the network's input size. Project costs, normalized so the budget is 1, are appended to this latent representation, and the network outputs a sigmoid score per project from which a feasible bundle is selected greedily. Training runs in two modes: implicit, where the cross-entropy loss compares the network's bundle to an optimal bundle from the target rule, and explicit, where the loss directly optimizes a smooth approximation of the welfare or representation score—the explicit mode being designed for datasets with many tied optima.
What would settle it
Run the network trained on synthetic data on published participatory budgeting elections from several cities other than Warsaw, comparing the welfare and representation ratios of its chosen bundles with those of the rule it was trained to imitate; if the ratios fall well short on average, or if the 30/70 AV/CC rule's average ratios on a fresh, diverse set of real instances diverge from Proportional Approval Voting's by more than the variance reported in the paper, the transfer and compromise claims would be falsified.
Extended reading notes
Core claim
The central discovery is that an aggregation rule for participatory budgeting can be embedded directly into a neural network's weights and then decoded on new, larger instances. Using a Set Transformer with a pooling-by-multihead-attention layer placed before the encoder, the network's input size depends only on the number of projects, not the number of voters, allowing training on instances with 10–900 voters and transfer to instances with up to 50,000. On the UNIQUE datasets, the learned rule attains total RMSE between 0.013 and 0.076 in the welfare-representation space, well below the 0.168–0.242 of sequential baselines, and it runs on the real-world Warsaw instances where the plain architecture exhausts GPU memory. The new observation is that a rule trained on a blend of 30% AV outcomes and 70% CC outcomes reproduces PAV's average welfare and representation ratios, giving a data-driven and closed-form rationale for PAV's balance of welfare and representation.
Load-bearing premise
The learned rules are trained on synthetic instances from four stylized generative models, so the approach rests on these models mimicking the approval patterns, project costs, and project interactions of real participatory budgeting settings where the rule would be deployed.
Editorial extensions
If this is right
- PB organizers could define a desired rule by supplying examples of outcomes, without knowing or stating the rule's formula.
- Rules learned on small synthetic instances transfer to large real elections, making the approach practical for municipal budgeting with tens of thousands of voters.
- The same trained network can be fine-tuned as objectives shift, so a community's aggregation rule can evolve without redesigning a rule from scratch.
- A compromise between competing objectives can be produced by mixing examples from each objective; the 30/70 AV/CC mix specifically recovers PAV's welfare-representation trade-off.
- Because inference with the network is fast, the learned rule is usable in real-time settings such as multi-winner voting in games or sensor-network decisions.
Reading between the lines
- If the approach generalizes beyond Warsaw, it suggests a paradigm in which aggregation rules are validated empirically by behavior rather than derived axiomatically; one could test whether other known rules, such as the Method of Equal Shares, are also recovered by particular AV/CC mixture levels.
- The paper's own caution that the network is a black box with no worst-case guarantees implies the safest deployment is as a decision-support tool for ordinary PB, with human veto, rather than as the final authority on public funds.
- The p=0.3 coincidence invites a direct experiment: train networks on AV/CC mixtures with p ranging from 0 to 1 in fine increments and check whether the welfare-representation curve is exactly the PAV curve at any other p, or whether 0.3 is special.
- A natural extension the paper leaves implicit is to train on mixtures of PAV and another proportional rule to see whether the learned compromise outperforms both parents on proportionality axioms such as justified representation.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a neural-network framework for learning participatory budgeting (PB) aggregation rules from labeled examples. The authors adapt the Set Transformer architecture by moving the pooling-by-multihead-attention (PMA) layer before the encoder, so that the network input is a fixed-size project representation regardless of the number of voters, and they introduce implicit (cross-entropy to an optimal bundle) and explicit (surrogate losses for welfare and representation) training modes. They evaluate the approach on synthetic datasets (Euclidean, One-vs-Many, Trade-Off AV, Trade-Off CC) and on real Warsaw PB data (2017–2021), reporting that the ST+PMA model learns AV, CC, and PAV rules on 'unique' datasets with low RMSE and generalizes to larger instances. The paper also learns mixture rules AV-CC-p and claims that a 30%-70% blend of AV and CC examples produces a rule that 'closely resembles' PAV, presented as a data-driven and closed-form rationale for PAV's welfare-representation balance.
Significance. If the results hold, the paper makes a useful contribution to data-driven social choice: it demonstrates that a reasonably simple neural architecture can learn standard PB rules from example optimal outcomes and can scale to the voter counts of real PB instances, which prior work on learning voting rules did not achieve for the PB setting. The architectural change (PMA before the encoder) is a practical engineering contribution, and the mixture-learning experiment, if properly supported, would offer an interesting perspective on the relationship between AV, CC, and PAV. The paper is honest about two limitations (black-box explainability and lack of worst-case guarantees), and the experimental setup is described in enough detail (dataset generators, hyperparameters, tie analysis) to be replicable. However, the central quantitative claims need strengthening: the headline RMSE tables lack uncertainty quantification, one of the four described model variants is omitted from results, and the PAV-resemblance claim is supported only by aggregate welfare/representation ratios rather than outcome-level comparisons.
major comments (4)
- [Section 7, Figure 2; Contribution (4)] The claim that AV-CC-0.3 'closely resembles' PAV and offers a 'data-driven rationale' for PAV is supported only by average welfare and representation ratios. The manuscript itself states that this 'does not mean that those two rules give the same outcome as PAV,' and average ratios can be matched by rules that select very different bundles. To make the resemblance claim load-bearing, the paper should report outcome-level similarity metrics (e.g., Jaccard overlap or rank correlation between funded bundles of AV-CC-0.3 and PAV) with confidence intervals, or explicitly weaken the claim to state that the average welfare/representation tradeoff of PAV is reproduced by the mixture on the evaluated datasets. In addition, the phrase 'closed-formula rationale' is misleading: the orange points in Figure 2 come from the ILP with objective p·welfare+(1−p)·representation, which is not the PAV score; the coincidence at p=0.3 is an empirical observation on these datasets, not a derivation.
- [Section 6, Tables 2 and 3; Appendix Tables 4 and 5] The RMSE values in Tables 2 and 3 are computed from dataset-level average welfare and representation ratios, with no error bars, confidence intervals, or repeated-seed information. The appendix tables show high per-instance variance for several cells, e.g., Table 5 reports OVM small AV implicit representation ratio 0.824 ± 0.249 and TOCC small CC implicit welfare ratio 0.095 ± 0.103; these large standard deviations mean that the aggregate RMSE may be dominated by a few instances or runs. The paper should report bootstrap intervals over instances and multiple training seeds, or otherwise quantify the uncertainty of the RMSE claims.
- [Section 6, first paragraph] The paper states that 'for brevity' it does not report the ST model with explicit learning because 'its performance was like that of Random.' This is a negative result for one of the four model variants the paper claims to evaluate, and its omission weakens the comparison, especially because the explicit method shows different behavior on TIED datasets. Please include the ST-explicit results (at least in the appendix) or provide a concrete summary of its performance, so readers can verify the claim and understand why this variant fails.
- [Section 5 and Appendix 1.A; Section 6.2] The generalization claim ('able to generalize from small-scale synthetic PB examples to large, real-world PB instances') rests on a single real-world collection (Warsaw) and on synthetic generators whose parameters are not varied in a sensitivity analysis. The paper should add cross-generator transfer experiments (e.g., train on EUC and test on OVM or TOCC, and vice versa) and, if feasible, evaluate on additional Pabulib datasets, to assess how sensitive the learned rules are to distribution shift. Without such experiments, a reader cannot tell whether the success on Warsaw reflects general representativeness of the synthetic benchmark or an accidental match to that particular city's instances.
minor comments (5)
- [Figure 2 caption] The caption says 'The first four points from the left correspond to p = 0, 0.01, 0.04, 0.8'; given the discussion of p ≤ 0.1, '0.8' is likely a typo for '0.08'. Please correct.
- [Section 7] The text 'Alongside AC-CC-p' should be 'Alongside AV-CC-p' to match the notation used everywhere else.
- [Section 4.2] The explicit representation loss uses a shifted sigmoid with parameters a=3 and b=6 that were chosen 'after testing a few candidates.' Please clarify how these values were selected and whether the results are robust to their choice, since the loss is an approximation of the true representation score.
- [Section 5 and Appendix 1.A] There are several typos and spacing inconsistencies, e.g., 'T rade-Off A V', 'TOA V', 'optimal soultions', 'mult-winner', and 'it possible possible to use it' in Section 8. A careful proofreading pass is needed.
- [Section 1.1] The notation introduces [k] but does not use it consistently; please either use it in the definitions of the scores or remove it.
Circularity Check
No significant circularity; the supervised learning setup and the explicitly qualified PAV analogy keep the derivation self-contained.
full rationale
The paper's central pipeline is supervised learning: networks are trained on PB instances labeled by optimal outcomes of AV, CC, or PAV, and then evaluated on held-out instances, including larger synthetic instances and real Warsaw data, using welfare and representation ratios. This is a standard fit-and-generalization setup, not a circular derivation: the evaluation metric is not identical to the training objective, and generalization to unseen and larger instances provides independent evidence that the network has learned the target rule rather than memorized the training labels. The AV-CC-0.3 claim is an empirical post-hoc observation that the average welfare and representation ratios of a learned mixture lie close to PAV's aggregate ratios; the paper explicitly disclaims outcome-level equivalence ('this does not mean that those two rules give the same outcome as PA V'), so the resemblance claim is not forced by construction. The only self-citation is to Fairstein et al. [11] for the welfare-versus-representation trade-off datasets; those datasets are described in detail in the current paper and are not used to assume the paper's conclusions. No fitted parameter is renamed as a prediction, no uniqueness theorem is imported from the authors' prior work, and the 'closed-formula' phrasing for PAV overstates what is an aggregate coincidence, but that is an interpretation/correctness concern rather than circularity.
Assumptions & free parameters
free parameters (1)
- sigmoid parameters a and b in explicit representation loss =
a=3, b=6
assumptions (4)
- domain assumption An aggregation rule can be approximated by a neural network trained on optimal outcomes of that rule.
- domain assumption The optimal outcomes used as labels are computed correctly by an exact solver or rigorous analysis.
- domain assumption Welfare and representation ratios are appropriate metrics to compare rules.
- ad hoc to paper The explicit representation loss with a shifted sigmoid is a valid differentiable surrogate.
Cite this review
Pith. "Pith review of Learning Aggregation Rules in Participatory Budgeting: A Data-Driven Approach." pith.science (2026). https://pith.science/paper/FYZ6FFCJ
@misc{pith2026241201864,
author = {Pith},
title = {Pith review of: Learning Aggregation Rules in Participatory Budgeting: A Data-Driven Approach},
year = {2026},
howpublished = {\url{https://pith.science/paper/FYZ6FFCJ}},
note = {Machine review of arXiv:2412.01864}
}
read the original abstract
Participatory Budgeting (PB) offers a democratic process for communities to allocate public funds across various projects through voting. In practice, PB organizers face challenges in selecting aggregation rules either because they are not familiar with the literature and the exact details of every existing rule or because no existing rule echoes their expectations. This paper presents a novel data-driven approach utilizing machine learning to address this challenge. By training neural networks on PB instances, our approach learns aggregation rules that balance social welfare, representation, and other societal beneficial goals. It is able to generalize from small-scale synthetic PB examples to large, real-world PB instances. It is able to learn existing aggregation rules but also generate new rules that adapt to diverse objectives, providing a more nuanced, compromise-driven solution for PB processes. The effectiveness of our approach is demonstrated through extensive experiments with synthetic and real-world PB data, and can expand the use and deployment of PB solutions.
Figures
Forward citations
Cited by 1 Pith paper
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What Voting Rules Actually Do: A Data-Driven Analysis of Multi-Winner Voting
A data-driven framework for counting axiom violations across preference distributions, with the claim that trained neural-network rules minimize violations better than traditional multi-winner rules.
Reference graph
Works this paper leans on
-
[1]
Advances in Neural Information Processing Systems 34, 8006–8017 (2021)
Anil, C., Bao, X.: Learning to elect. Advances in Neural Information Processing Systems 34, 8006–8017 (2021)
work page 2021
-
[2]
In: Pathways Between Social Science and Computational Social Science, pp
Aziz, H., Shah, N.: Participatory budgeting: Models and approaches. In: Pathways Between Social Science and Computational Social Science, pp. 215–236, Springer (2021)
work page 2021
-
[3]
Boixel, A., Endriss, U., Nardi, O., et al.: Displaying justifications for collective decisions. In: IJCAI, pp. 5892–5895 (2022)
work page 2022
-
[4]
Environment and urbanization 16(1), 27–46 (2004)
Cabannes, Y.: Participatory budgeting: a significant contribution to participatory democracy. Environment and urbanization 16(1), 27–46 (2004)
work page 2004
-
[5]
In: Proceedings of the AAAI Conference on Artificial Intelligence, vol
Caragiannis, I., Fehrs, K.: The complexity of learning approval-based multiwinner voting rules. In: Proceedings of the AAAI Conference on Artificial Intelligence, vol. 36, pp. 4925–4932 (2022)
work page 2022
-
[6]
American Political Sci- ence Review 77(3), 718–733 (1983)
Chamberlin, J.R., Courant, P.N.: Representative deliberations and representative decisions: Proportional representation and the borda rule. American Political Sci- ence Review 77(3), 718–733 (1983)
work page 1983
-
[7]
In: Twenty-Ninth AAAI Conference on Artificial Intelligence (2015)
Doucette, J.A., Larson, K., Cohen, R.: Conventional machine learning for social choice. In: Twenty-Ninth AAAI Conference on Artificial Intelligence (2015)
work page 2015
-
[8]
In: Proceedings of the AAAI Conference on Artificial Intelligence, vol
Elkind, E., Faliszewski, P., Laslier, J.F., Skowron, P., Slinko, A., Talmon, N.: What do multiwinner voting rules do? an experiment over the two-dimensional euclidean domain. In: Proceedings of the AAAI Conference on Artificial Intelligence, vol. 31 (2017)
work page 2017
Show all 46 references
-
[9]
CUP Archive (1984)
Enelow, J.M., Hinich, M.J.: The spatial theory of voting: An introduction. CUP Archive (1984)
1984
-
[10]
arXiv preprint arXiv:2106.05360 (2021)
Fairstein, R., Meir, R., Gal, K.: Proportional participatory budgeting with sub- stitute projects. arXiv preprint arXiv:2106.05360 (2021)
2021 arXiv
-
[11]
representation in participatory budgeting
Fairstein, R., Reshef, M., Vilenchik, D., Gal, K.: Welfare vs. representation in participatory budgeting. In: Proceedings of the 22th AAMAS, p. 409–417 (2022)
2022
-
[12]
Collective Decisions: Theory, Algorithms And Decision Support Systems pp
Faliszewski, P., Szufa, S., Talmon, N.: Optimization-based voting rule design: The closer to utopia the better. Collective Decisions: Theory, Algorithms And Decision Support Systems pp. 17–51 (2022)
2022
-
[13]
Firebanks-Quevedo, D.: Machine Learning? In MY Election? It’s More Likely Than You Think: Voting Rules via Neural Networks. Ph.D. thesis, Oberlin College (2020)
2020
-
[14]
In: Companion of the 2024 on ACM Inter- national Joint Conference on Pervasive and Ubiquitous Computing, pp
Hashemi, M., Darejeh, A., Cruz, F.: A user-centric exploration of axiomatic ex- plainable ai in participatory budgeting. In: Companion of the 2024 on ACM Inter- national Joint Conference on Pervasive and Ubiquitous Computing, pp. 126–130 (2024)
2024
-
[15]
In: Proceedings of the 29th International Joint Conference on Artificial Intelligence (IJCAI), pp
Jain, P., Sornat, K., Talmon, N.: Participatory budgeting with project interactions. In: Proceedings of the 29th International Joint Conference on Artificial Intelligence (IJCAI), pp. 386–392 (2020)
2020
-
[16]
arXiv preprint arXiv:2305.01769 (2023)
Janeczko, L., Faliszewski, P.: Ties in multiwinner approval voting. arXiv preprint arXiv:2305.01769 (2023)
2023 arXiv
-
[17]
In: 2016 3rd International Conference on Systems and Informatics (ICSAI), pp
Jiao, P., Xu, K., Sun, L.: Diversity voting and its application in real-time strategy games multi-objective optimization decision-making behavior modeling. In: 2016 3rd International Conference on Systems and Informatics (ICSAI), pp. 552–559, IEEE (2016) Title Suppressed Due t...
2016
-
[18]
In: Multi-Agent Systems and Agreement Technologies, pp
Kujawska, H., Slavkovik, M., R¨ uckmann, J.J.: Predicting the winners of borda, kemeny and dodgson elections with supervised machine learning. In: Multi-Agent Systems and Agreement Technologies, pp. 440–458, Springer (2020)
2020
-
[19]
In: Inter- national conference on machine learning, pp
Lee, J., Lee, Y., Kim, J., Kosiorek, A., Choi, S., Teh, Y.W.: Set transformer: A framework for attention-based permutation-invariant neural networks. In: Inter- national conference on machine learning, pp. 3744–3753, PMLR (2019)
2019
-
[20]
Social Choice and Welfare pp
Lu, X., Peters, J., Aziz, H., Bei, X., Suksompong, W.: Approval-based voting with mixed goods. Social Choice and Welfare pp. 1–35 (2024)
2024
-
[21]
Orsted, H.C., Forchhammer, G., Steenstrup, J.J.S.: Oversigt over det Kongelige Danske Videnskabernes Selskabs Forhandlinger (1894)
-
[22]
Advances in Neural Information Processing Systems 34, 12726–12737 (2021)
Peters, D., Pierczy´ nski, G., Skowron, P.: Proportional participatory budgeting with additive utilities. Advances in Neural Information Processing Systems 34, 12726–12737 (2021)
2021
-
[23]
Advances in Neural Information Processing Systems 33, 1525–1534 (2020)
Peters, D., Procaccia, A.D., Psomas, A., Zhou, Z.: Explainable voting. Advances in Neural Information Processing Systems 33, 1525–1534 (2020)
2020
-
[24]
Artificial Intelligence 173(12-13), 1133–1149 (2009)
Procaccia, A.D., Zohar, A., Peleg, Y., Rosenschein, J.S.: The learnability of voting rules. Artificial Intelligence 173(12-13), 1133–1149 (2009)
2009
-
[25]
arXiv preprint arXiv:2303.00621 (2023)
Rey, S., Maly, J.: The (computational) social choice take on indivisible participa- tory budgeting. arXiv preprint arXiv:2303.00621 (2023)
2023 arXiv
-
[26]
Information Processing Letters 42(3), 173–177 (1992)
Sarkar, U., Chakrabarti, P., Ghose, S., De Sarkar, S.: A simple 0.5-bounded greedy algorithm for the 0/1 knapsack problem. Information Processing Letters 42(3), 173–177 (1992)
1992
-
[27]
IEEE transactions on neural networks 20(1), 61–80 (2008)
Scarselli, F., Gori, M., Tsoi, A.C., Hagenbuchner, M., Monfardini, G.: The graph neural network model. IEEE transactions on neural networks 20(1), 61–80 (2008)
2008
-
[28]
arXiv preprint arXiv:2009.02690 (2020)
Skowron, P., Slinko, A., Szufa, S., Talmon, N.: Participatory budgeting with cu- mulative votes. arXiv preprint arXiv:2009.02690 (2020)
2020 arXiv
-
[29]
New Political Science 36(2), 193–218 (2014)
Stewart, L.M., Miller, S.A., Hildreth, R., Wright-Phillips, M.V.: Participatory budgeting in the united states: a preliminary analysis of chicago’s 49th ward ex- periment. New Political Science 36(2), 193–218 (2014)
2014
-
[30]
arXiv preprint arXiv:2012.06539 (2020)
Stolicki, D., Szufa, S., Talmon, N.: Pabulib: A participatory budgeting library. arXiv preprint arXiv:2012.06539 (2020)
2020 arXiv
-
[31]
New Political Science 39(1), 67–75 (2017)
Su, C.: From porto alegre to new york city: Participatory budgeting and democ- racy. New Political Science 39(1), 67–75 (2017)
2017
-
[32]
In: Proceedings of the AAAI Conference on Artificial Intelligence, vol
Talmon, N., Faliszewski, P.: A framework for approval-based budgeting methods. In: Proceedings of the AAAI Conference on Artificial Intelligence, vol. 33, pp. 2181–2188 (2019)
2019
-
[33]
Wireless Communications and Mobile Computing 2022 (2022)
Wu, X., Chen, Z., Zhong, Y., Zhu, H., Chen, X., Zhang, P., et al.: Multiwin- ner voting for energy-efficient mobile sink rendezvous selection in wireless sensor network. Wireless Communications and Mobile Computing 2022 (2022)
2022
-
[34]
884–885 (2021)
Xia, L.: How likely are large elections tied? In: Proceedings of the 22nd ACM Conference on Economics and Computation, pp. 884–885 (2021)
2021
-
[35]
Xu, K., Hu, W., Leskovec, J., Jegelka, S.: How powerful are graph neural networks? arXiv preprint arXiv:1810.00826 (2018)
2018 arXiv
-
[36]
Advances in neural information processing systems 30 (2017)
Zaheer, M., Kottur, S., Ravanbakhsh, S., Poczos, B., Salakhutdinov, R.R., Smola, A.J.: Deep sets. Advances in neural information processing systems 30 (2017)
2017
-
[37]
In: 2017 Conference for E-Democracy and Open Government (CeDEM), pp
Zepic, R., Dapp, M., Krcmar, H.: Participatory budgeting without participants: Identifying barriers on accessibility and usage of german participatory budgeting. In: 2017 Conference for E-Democracy and Open Government (CeDEM), pp. 26– 35, IEEE (2017) 20 Roy Fairstein, Dan Vile...
2017
-
[38]
Voters and projects coordinates (The location on a [0 , 1]X[0, 1] map of each voter and project)
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[39]
Number of projects each voter approves ( k). The first three items are sampled uniformly, such that the number of voters is in range according to the dataset size as described in Table 1, the number of projects in range [20 , 50] and the budget in range [10000 , 250000]. Proje...
-
[40]
All costs are possible equally - the costs are sampled for uniform distribution in range [100 , 100000]
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[41]
There are many cheap projects and a few expensive - for this purpose an exponential distribution is used, where the minimal project cost is taken at random from (10 , 20, 500, 1000) and the projects mean cost is taken at random from (10000 , 15000, 30000)
-
[42]
V oters and projects coordinates Two types of distributions were chosen to simulate different situations (each instance have equal probability to be from each distribution):
There are few projects that are cheap or expensive - a normal distribution is used N ( budget 2 , budget 5 ). V oters and projects coordinates Two types of distributions were chosen to simulate different situations (each instance have equal probability to be from each distribution):
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[43]
Spreading equally in the entire map - the location is sampled uniformly in the entire map
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[44]
Notice that that any combinations for the voters and projects is valid,e.g
More citizen or projects closer to the city center - the location is sampled us- ing normal distribution ∼ N (0.5, sigma), where sigma ∈ [0.1, 0.2, 0.3] taken in random (creating different city densities). Notice that that any combinations for the voters and projects is valid,...
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[45]
Title Suppressed Due to Excessive Length 21
It is equally likely for a voter to approve any number of projects - the number of approved projects sampled uniformly from kv ∼ U (1, 0.75|P |). Title Suppressed Due to Excessive Length 21
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[46]
In the instance creating, each voter approve the kv projects that are the closest to his location
It is not likely for voters approve either a few projects or most of the projects - sampled from normal distributionkv ∼ N ( |P | scale , 3), where scale ∈ [3, 2.5, 2]. In the instance creating, each voter approve the kv projects that are the closest to his location. 1.B Detai...
Reviewed August 12, 2026 · model on record in the stance chip above.
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