A method, computer, and recording medium storing a program are provided which, based on local optimal solutions, more efficiently calculate an optimal global optimal solution in a global operating area. System calculates the global optimal solution by solving, using a genetic algorithm based on the local optimal solutions and the initial values, an equation, which should be satisfied by the plurality of design variables, by obtaining the plurality of combinations of design variables composing local optimal solutions for each design variable respectively calculated for each of a plurality of combinations of a plurality of operating states, and by obtaining initial values for the plurality of combinations of design variables used for calculating the global optimal solution.