This repository hosts a collection of programs written by team Probably in Control (part of the Summer 2018 HEATlab group). This work resulted in a publication at the 29th International Conference of Automated Planning and Scheduling (ICAPS-19) titled "Quantifying Degrees of Controllability for Temporal Networks with Uncertainty". A pre-print is available here.

These files were migrated from the repository for Robotbrunch, a previous HEATlab team. The programs here serve to

• generate STNUs, both randomly and from provided PSTN datasets,
• compute metrics related to controllability on STNUs, and
• simulate dispatch on STNUs.

The dataset folder hosts JSON representations of STNUs used in our research. These STNUs were constructed from the ROVERS and CAR-SHARING PSTNs, made by (Santana et. al. 2016) and available here, by replacing distributions with finite intervals over all contingent edges.

Each STNU is encoded by a list of nodes and constraints between those nodes. All 452 STNUs in the dataset/dynamically_controllable directory are dynamically controllable while the 169 STNUs in the dataset/uncontrollable directory are consistent, but not dynamically controllable.

This dataset of networks is referenced in the paper our team submitted to ICAPS 2019.

Files throughout the project are commented in doxygen style.

The stn folder contains files describing an STN class (which is really a class for STNUs, and more generally could be easily extended to represetn PSTNs) and converting between the class and JSON representations of networks. The remaining programs are not organized in any particular way. Because of this, in the comments that follow we often describe as a function taking in an "STN" when it really also works with STNUs as input.

Implements conflict generating algorithms for checking if a STNU is dynamically controllable (DC). If the network is not DC, there are functions for reporting the "conflicts" that prevent the network from achieving controllability.

Implements the DCDijkstra algorithm described in (Williams 2017).

Implements a dispatch strategy and associated simulation for STNUs, based off Algorithm 2 from (Nilsson 2014).

This strategy should always succeed for dynamically controllable STNUs. It works by first leveraging a conversion to the DC_STN class to infer wait constraints, and then following early execution.

Known limitation: this process is only guaranteed to work in cases where the conversion infers all wait constraints. This means that care should be taken to make sure this this dispatch strategy is only run on networks for which the dc_stn.py computes all necessary constraints. In particular, the networks in the dataset/uncontrollable network satisfy this property.

Uses PuLP module to set up and solve several different LPs. These LPs are primarily attempts at linearizing the calculation for degree of strong controllability. The main structure of the constraints remains the same accross most of the programs, but there are many different types of objective functions used.

This files contains 4 different LPs (Original LP has two different kinds objectives).

• Original LP (with naive objective function): In this LP, we are minimizing the sum of contingent intervals shrinked.
• Original LP: In this LP, we are minimizing the sum of contingent intervals shrinked divided by original length of the contingent intervals.
• Proportion LP: In this LP, we are shrinking all contingent edges by the same proportion, and we are minimizing the proportion shrinked.
• Maximin LP: In this LP, we are maximizing the minimum amount we can shrink from a contingent edge.
• Minimax LP: In this LP, we are minimizing the maximum amount we can shrink from a contingent edge.

Through experiments, we discovered that the Original LP was the best approximation for the degree of strong controllability. This method is referred to in our paper as the DSC-LP.

Stores functions that, given conflicts from non-DC network, return the predicted probability of successful dispatch on those networks.

The approximation here is an application of CLT to sums of uniformly distributed random variables.

Using the routines from algorithm.py and LP.py, defines various different ways of selecting "maximal" subintervals.

The approaches for computing subintervals in the strong controllability case involve using solutions from some LPs. In the dynamic controllability case, the main approach implemented is the optimalRelax function, which is a very straightforward algorithm (with O(k*log k) complexity, if k is the number of edges in the conflict) that finds the true maximum subintervals (in the sense of maximizing resulting volume while ensuring the conflict is resolved).

Defines STN, Edge, and Vertex classes.

A Vertex represents an event in an STN. It is encoded as a single node with a unique integer ID.

An Edge represents a constraint in an STN. It is encoded as a pair of vertex IDs labeled with an interval and type. The type designates an edge as a requirement (stc) or contingent (stcu) edge.

An STN consists of events with constraints in between events. An STN object is encoded as set of Vertices with Edges between some pairs of vertices.

In general, a Vertex with ID zero is treated as the zero-timepoint.

Provides functions to create STN objects from input JSON files.

An older file inherited from previous teams. Builds a DC_STN class that represents STNUs with an aim of manipulating the associated labeled distance graph. Implements the DC checking algorithm described in (Morris 2003) which works by inferring wait constraints between events. Also has a function for checking if STNs are consistent or not.

Computes and plots empirical results, mainly related to strong controllability.

Leverages functions from LP.py, dispatch.py, and relax.py to measure approximate and exact degrees of strong controllability, approximate degrees of dynamic controllability, and true success rates with different dispatch strategies. Comtains some methods for plotting these results as well.

A file that makes use of the plotly module to make some nice graphs of the results outputted by empirical.py.

A short file for computing correlations between some of the sets of data stored in the result folder.

Attempts at writing early and late strategies for dispatch on STNUs. This program did not really end up getting used, since the attempts at implementing early and late strategies here are incorrect. Instead, we only used the simulation presented in dispatch.py.

Holds a few helpful functions, which are called by other programs.

Provides

• STNtoDCSTN: a function for converting from STN objects to DC_STN objects
• normal: a function for getting STNUs in normal form (that is, all contingent edges have lower bound zero)
• PriorityQueue: a class implementing a standard min-heap

A python program to take in AMPL model files and convert them to an XML format that can be submitted to the NEOS server.

Given an STNU, builds the corresponding optimization problem for computing the degree of strong controllability for the network.

The output is an AMPL file. The objective function is the logarithm of the product of the lengths of contingent subintervals.

A NEOS Python client (made available by the NEOS server) that has been mildly modified. This is used to submit optimization problems to NEOS, and then extract the values achieved by the objective function once the jobs are finished.

This folder contains several JSON files storing results we found related to degree of controllability, empirical success rates for dispatch, and solutions to nonlinear optimization problems.

The Summer 2018 HEATlab consisted of teams Probably in Control, Acrobotics, and Robot Luncheon. The former two are the spiritual successors to the 2017 HEATlab Polybots team, while the latter is the evolution and extension of 2017 HEATlab team Robot Brunch. All teams worked at Harvey Mudd College under the supervision of Professor Jim Boerkoel as part of the HMC CS department's "summer of CS".

• Probably in Control ~ Team {Maggie Li, Savana Ammons, Shyan Akmal}

  • Explored the geometry of STNUs and degrees of controllability
  • A pre-print of our work, published in ICAPS-19, can be accessed here.

• Acrobotics ~ Team VivaJoon OjhaLee

  • Explored the durability of schedules in STNs and developed sumobot mascots
  • A pre-print of their work, published in ICAPS-19, can be found here.

• Robot Luncheon ~ Senior lab member Jordan R. Abrahams

  • Designed and tested the DREAM algorithm for PSTN dispatch
  • A pre-print of his and his collaborators' work, published in ICAPS-19, can be found here.

  License

  This project is licensed under the terms of the MIT license.