Source code for cobra.flux_analysis.fastcc

# -*- coding: utf-8 -*-

"""Provide an implementation of FASTCC."""

from __future__ import absolute_import

from optlang.symbolics import Zero
from six import iteritems

from cobra.flux_analysis.helpers import normalize_cutoff

[docs]def _find_sparse_mode(model, rxns, flux_threshold, zero_cutoff): """Perform the LP required for FASTCC. Parameters ---------- model: cobra.core.Model The cobra model to perform FASTCC on. rxns: list of cobra.core.Reactions The reactions to use for LP. flux_threshold: float The upper threshold an auxiliary variable can have. zero_cutoff: float The cutoff below which flux is considered zero. Returns ------- result: list The list of reactions to consider as consistent. """ if rxns: obj_vars = [] vars_and_cons = [] prob = model.problem for rxn in rxns: var = prob.Variable( "auxiliary_{}".format(, lb=0.0, ub=flux_threshold ) const = prob.Constraint( rxn.forward_variable + rxn.reverse_variable - var, name="constraint_{}".format(, lb=0.0, ) vars_and_cons.extend([var, const]) obj_vars.append(var) model.add_cons_vars(vars_and_cons) model.objective = prob.Objective(Zero, sloppy=True) model.objective.set_linear_coefficients({v: 1.0 for v in obj_vars}) model.optimize(objective_sense="max") result = [rxn for rxn in model.reactions if abs(rxn.flux) > zero_cutoff] else: result = [] return result
[docs]def _flip_coefficients(model, rxns): """Flip the coefficients for optimizing in reverse direction.""" # flip reactions for rxn in rxns: const = model.constraints.get("constraint_{}".format( var = model.variables.get("auxiliary_{}".format( coefs = const.get_linear_coefficients(const.variables) const.set_linear_coefficients( {k: -v for k, v in iteritems(coefs) if k is not var} ) # flip objective objective = model.objective objective_coefs = objective.get_linear_coefficients(objective.variables) objective.set_linear_coefficients({k: -v for k, v in iteritems(objective_coefs)})
[docs]def fastcc(model, flux_threshold=1.0, zero_cutoff=None): r""" Check consistency of a metabolic network using FASTCC [1]_. FASTCC (Fast Consistency Check) is an algorithm for rapid and efficient consistency check in metabolic networks. FASTCC is a pure LP implementation and is low on computation resource demand. FASTCC also circumvents the problem associated with reversible reactions for the purpose. Given a global model, it will generate a consistent global model i.e., remove blocked reactions. For more details on FASTCC, please check [1]_. Parameters ---------- model: cobra.Model The constraint-based model to operate on. flux_threshold: float, optional (default 1.0) The flux threshold to consider. zero_cutoff: float, optional The cutoff to consider for zero flux (default model.tolerance). Returns ------- cobra.Model The consistent constraint-based model. Notes ----- The LP used for FASTCC is like so: maximize: \sum_{i \in J} z_i s.t. : z_i \in [0, \varepsilon] \forall i \in J, z_i \in \mathbb{R}_+ v_i \ge z_i \forall i \in J Sv = 0 v \in B References ---------- .. [1] Vlassis N, Pacheco MP, Sauter T (2014) Fast Reconstruction of Compact Context-Specific Metabolic Network Models. PLoS Comput Biol 10(1): e1003424. doi:10.1371/journal.pcbi.1003424 """ zero_cutoff = normalize_cutoff(model, zero_cutoff) irreversible_rxns = [rxn for rxn in model.reactions if not rxn.reversibility] rxns_to_check = irreversible_rxns with model: rxns_to_keep = _find_sparse_mode( model, rxns_to_check, flux_threshold, zero_cutoff ) rxns_to_check = list(set(model.reactions).difference(rxns_to_keep)) while rxns_to_check: with model: new_rxns = _find_sparse_mode( model, rxns_to_check, flux_threshold, zero_cutoff ) rxns_to_keep.extend(new_rxns) # this condition will be valid for all but the last iteration if list(set(rxns_to_check).intersection(rxns_to_keep)): rxns_to_check = list(set(rxns_to_check).difference(rxns_to_keep)) else: rxns_to_flip = list(set(rxns_to_check).difference(irreversible_rxns)) _flip_coefficients(model, rxns_to_flip) sol = model.optimize(min) to_add_rxns = sol.fluxes.index[sol.fluxes.abs() > zero_cutoff].tolist() rxns_to_keep.extend( [model.reactions.get_by_id(rxn) for rxn in to_add_rxns] ) # since this is the last iteration, it needs to break or else # it will run forever since rxns_to_check won't be empty break consistent_rxns = set(rxns_to_keep) # need the ids since Reaction objects are created fresh with model.copy() rxns_to_remove = [ for rxn in set(model.reactions).difference(consistent_rxns) ] consistent_model = model.copy() consistent_model.remove_reactions(rxns_to_remove, remove_orphans=True) return consistent_model