FBA objective function more than one reaction

  • cbasile

    My name is Christian ,  I am trying to do some flux balance analisis using Cobra, however, I am struggling because of the following:

    It seems that in Cobra python you can define an objective function only , by choosing just one reaction.What I will like to do is to minimize  a  

    min (   ' ) = min (v1 + v2 + v3 + v4)

    Sv = 0 ,   S being n(metabolite) by m ( reaction)

    where where v are all the vm's , n being the number of fluxes or reaction in this case.

    Some vm (specific ones) I want to constrained them to a number), both lower and upper bound,

    So, far i think that Cobra is capable of doing this, but I dont see any documentation on trying to do this. All the examples are just minimizing  a    just      c1 vm     c1  being a coefficient  with 1x1 dimension, and vm being 1x1 also, that is great, but I dont want this, I want to minimize a 1x4 4x1  =  1x1 =   v1 + v2 + v3 + v4 ,    single objective function,

    I would deeply appreciate help for this,

    Thank you very much,


    I would deeply appreciate your help,

    I am very excited to use your software,



  • Daniel Hyduke
    Daniel Hyduke

    What should work is something like this:

    #Load a cobra model
    from cobra.test import create_test_model
    model = create_test_model()

    #Set the linear coefficients all to 0

    #Set linear objectives for a set of reactions
    the_reactions = model.reactions
    the_coefficients =
    for the_reaction, the_coefficient in zip(the_reactions, the_coefficients):
        the_reaction.objective_coefficient = the_coefficient

    #optimize the model

    print model.solution.f

    #Print the flux values
    for the_reaction in the_reactions:
        print the_reaction.id + ' = ' + repr(model.solution.x_dict)

    P.S. I think we'll be adding a function soon to attach the results directly to the model variables; i.e., you'll be able to access the flux coefficients by entering the_reaction.x as opposed to model.solution.x_dict.