FBA aligned to ModelPruner (using sparce matrices)

setup.py

xbanalysis/model/xba_model.py

xbanalysis/problems/__init__.py

xbanalysis/problems/fba_problem.py

xbanalysis/problems/rba_problem.py

xbanalysis/problems/rba_problem_coo.py

xbanalysis/solvers/__init__.py

xbanalysis/solvers/glpk_linear_problem.py

xbanalysis/solvers/lp_problem.py