Path4gmns

v0.7.4 comes with bug and issue fixes.

1. fix bug on zero divisor in update_generalized_link_cost();
2. fix wrong exception message in read_links();
3. remove the legacy utf-8 encoding requirement on instances of open(), which was inherited from DTALite in Python (i.e., the code base leading to Path4GMNS).

Other updates include,

4. add a concise guideline on how to contribute to Path4GMNS in README;
5. provide references in README on the Path-based UE;
6. use single quotes consistently across the project.

v0.7.3 enhances the previous release with time-dependent accessibility evaluation, potential issue resolution on inconsecutive zone id's, and bug fix regarding connectors in DTALite.

Time-dependent Accessibility Evaluation
1. Evaluate any periodic accessibility using its corresponding VDF_fftt in link.csv;
2. Obtain periodic accessible nodes and links using using its corresponding VDF_fftt in link.csv;
3. Output shortest path distance info in addition path travel time (i.e., accessibility) in accessibility.csv;
4. Include zone coordinates in accessibility.csv and accessibility_aggregated.csv.

Potential Issue Resolution on Inconsecutive Zone ID's
As zone_id's are not necessarily consecutive numbers starting from zero, the previous implementation using list (with assumed consecutive zone id as index) would not go through if the assumption is violated.

Bug Fix on Connectors in DTALite
For an outgoing connector, its zone_seq_no_for_outgoing_connector should be the corresponding zone seq no of zone_org_id associated with the from node. See commit 5c65ff in DTALite for details.

Other Changes
1. Replace hard-coded 0.001, 0.0001 and similar with a constant SMALL_DIVISOR;
2. Replace the initial value of least_gradient_cost with MAX_LABEL_COST;
3. Change MAX_LABEL_COST to 999999;
4. Update path_engine so that MAX_LABEL_COST can be passed as a parameter to it at run-time.

v0.7.2 features new functionalities, bug fixes and new interface.

New Functionalities
1. Find shortest path between two (different) nodes under a specific mode;
2. Find paths for all agents under a specific mode.

Bug Fixes
1. Fix bug in the C++ path engine that all modes (which is defined by "all" and specifying that some links are open to all nodes) were not functioning right. See commit 5c65ff2 for details.
2. Fix bug that ats (agent types) were not correctly set up according to argument multimodal in evaluate_accessibility(), which leaded to all zeros for non-target mode in aggregated_accessibility.csv;

New Interface
Introduce **perform_column_generation()** to replace **perform_network_assignment()**. Some users were reported to use perform_network_assignment() to perform other types of traffic assignments besides the path-based UE (as somehow implied by the function name and its argument list). Deprecate **perform_network_assignment()** from now on but keep it as legacy support.

v0.7.1 comes with potential issue fixes as below.

1. Adopt PEP8 on comparisons to None in utils.py. The previous implementation would discard attributes with value 0;
2. Add connectivity check for each OD pair. Raise exception if there are no valid OD volumes/demands;
3. For DTALite, if the link type of a link in link.csv is not defined settings.csv, set its value as 2 (i.e., Major arterial). Otherwise, execution of DTALite would be terminated due to undefined link types. Recompile DTALite with this change for Windows, Linux, and macOS. The details can be found under commit 8f3ced5 in https://github.com/jdlph/DTALite/;
4. Add special output to find_shortest_path() if no path exists between two different nodes;
5. Print out directory information for the following output functions, i.e., output_columns(), output_link_performance(), output_agent_paths(), _output_accessibility(), and _output_accessibility_aggregated().

v0.7.0 fixes known bugs and potential issues in v0.7.0a1, replaces the accessibility evaluation implementation, and introduces new functionalities.

Known Bugs and Potential Issues Fix
1. Fix bug on duplicate link when printing out path sequence in function output_path_sequence();
2. Fix column incompatibility between Path4GMNS and DTALite, which results into failure of loading columns from DTALite;
3. Fix potential memory issue when evaluating accessibility for large-scale networks (see the following for details);
4. Fix several typos on accessibility and assignment.

New Lightweight and Faster Implementation for Accessibility Evaluation
The new implementation uses virtual centroids and connectors to facilitate the shortest path calculation between zones rather than set up virtual demands between any two different zones and maintain a column pool. It resolves the potential memory issue and leads to a much faster evaluation process. Its running speed is **9X faster** than v0.7.0a1.

New Functionalities
1. Get accessible nodes and links given a time budget and a transportation mode;
2. Print out path distance in find_shortest_path() and get_agent_node_path();
3. Output unique agent paths to a csv file through output_agent_paths();
4. Let users decide whether to include geometry information in the output file for output_agent_paths() and output_columns().

Others

v0.7.0a1 comes with new functionalities, improved performance, and more robust input loading.

**New Functionalities:**
1. Support of link allowed uses in class Link and the routing engine;
2. Multimodal accessibility evaluation;
3. Loading columns from previous runs and continue the column generation procedure;
4. A helper function to download the sample data set with six different networks.

**Improved Performance:**
- Around 15% reduction in CPU time for the column generation procedure (test against v0.6.0 using 20 assignment iterations and 20 column generation iterations for the Chicago Sketch Network).

**More Robust Input Loading:**
- Enhance exception handlings to deal with records are empty or not desired types when loading inputs.