A method includes: calculating a change amount of energy of an Ising model, the change amount being caused when values of four states are changed, for each of a plurality of first states having a value of 0 before change, so as to satisfy a constraint that a sum of values of states included in each row is 1, and a sum of values of states included in each column is 1, when N (an integer of 2 or larger) squared state variables included in an evaluation function representing the energy of the Ising model are arrayed in N rows and N columns; selecting the four states allowed to change by using the change amount calculated for each of the plurality of first states, and outputting identification information for identifying the four states; and updating values of the four states allowed to change by using the identification information.