varying objective function in geometric programming

I am trying to maximize the secrecy capacity of a relaying network with five design variables. I am using GGPLAB to solve the problem through iterative geometric programming. The objective function is to be updated every iteration. GP solver accepts the objective function if I added it manually feom the previous iteration. But if I dirct the code to a function to calculate the new objective function I get error message:

Error using sym/eval

Too many input arguments.

Error in gpproblem>standardize (line 318)

obj = eval( obj, {'' []} );

Error in gpproblem (line 135)

[r.std_obj new_con new_vars] =

standardize(r.obj,r.new_gpvars_count);

Error in gpsolve (line 44)

gp_problem_obj = gpproblem(obj, constr, flag);

Error in GGPLAB_theta_c (line 79)

[min_c solution status] = gpsolve(obj,constr,'min');

I cannot keep doing it manually . Any ideas?

[Maymoona Hayajneh]

The objective functionis recognized as a generalized posynomial when i copy paste it to the code.