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Release v2.0.0

Release Date: March 29, 2025

🚀 Major Framework Changes

  • Migration from Pyomo to Linopy: Completely rebuilt the optimization foundation to use Linopy instead of Pyomo
    • Significant performance improvements, especially for large models
    • Internal useage of linopys mathematical modeling language
  • xarray-Based Data Architecture: Redesigned data handling to rely on xarray.Dataset throughout the package for:
    • Improved solution representation and analysis
    • Enhanced time series management
    • Consistent serialization across all elements
    • Reduced file size and improved performance
  • Saving and restoring unsolved Models: The FlowSystem is now fully serializable and can be saved to a file.
    • Share your work with others by saving the FlowSystem to a file
    • Load a FlowSystem from a file to extend or modify your work

🔧 Key Improvements

Model Handling

  • Extend every flixopt model with the linopy language: Add any additional constraint or variable to your flixopt model by using the linopy language.
  • Full Model Export/Import: As a result of the migration to Linopy, the linopy.Model can be exported before or after the solve.
  • Improved Infeasible Model Handling: Added better detection and reporting for infeasible optimization models
  • Improved Model Documentation: Every model can be documented in a .yaml file, containing human readable mathematical formulations of all variables and constraints. THis is used to document every Calculation.

Calculation Results and documentation:

The CalculationResults class has been completely redesigned to provide a more streamlined and intuitive interface. Accessing the results of a Calculation is now as simple as: 

fx.FullCalculation('Sim1', flow_system)
calculation.solve(fx.solvers.HighsSolver())
calculation.results  # This object can be entirely saved and reloaded to file without any information loss
This access doesn't change if you save and load the results to a file or use them in your script directly!

  • Improved Documentation: The FlowSystem as well as a model Documentation is created for every model run.
  • Results without saving to file: The results of a Calculation can now be properly accessed without saving the results to a file first.
  • Unified Solution exploration: Every Calculation has a Calculation.results attribute, which accesses the solution. This can be saved and reloaded without any information loss.
  • Improved Calculation Results: The results of a Calculation are now more intuitive and easier to access. The CalculationResults class has been completely redesigned to provide a more streamlined and intuitive interface.

Data Management & I/O

  • Unified Serialization: Standardized serialization and deserialization across all elements
  • Compression Support: Added data compression when saving results to reduce file size
  • to_netcdf/from_netcdf Methods: Added for FlowSystem and other core components

Details

TimeSeries Enhancements

  • xarray Integration: Redesigned TimeSeries to depend on xr.DataArray
  • datatypes: Added support for more datatypes, with methods for conversion to TimeSeries
  • Improved TimeSeriesCollection: Enhanced indexing, representation, and dataset conversion
  • Simplified Time Management: Removed period concepts and focused on timesteps for more intuitive time handling

📚 Documentation

  • Improved documentation of the FlixOpt API and mathematical formulations
  • Google Style Docstrings: Updated all docstrings to Google style format

🔄 Dependencies

  • Linopy: Added as the core dependency replacing Pyomo
  • xarray: Now a critical dependency for data handling and file I/O
  • netcdf4: Dependency for fast and efficient file I/O

Dropped Dependencies

  • pyomo: Replaced by linopy as the modeling language

📋 Migration Notes

This version represents a significant architecture change. If you're upgrading:

  • Code that directly accessed Pyomo models will need to be updated to work with Linopy
  • Data handling now uses xarray.Dataset throughout, which may require changes in how you interact with results
  • The way labels are constructed has changed throughout the system
  • The results of calculations are now handled differently, and may require changes in how you access results
  • The framework was renamed from flixOpt to flixopt. Use import flixopt as fx.

For complete details, please refer to the full commit history.

Installation

pip install flixopt==2.0.0

Upgrading

pip install --upgrade flixopt