PURPOSE: To prevent the occurrence of abnormal arrangement during the progression of processing and to maintain consistency by evading the duplication and omission of the same symbol in the arrangement of intermediate solution when exchanging information between processors.
CONSTITUTION: The intermediate solution of a problem is expressed in the arrangement of the sent of a symbol, for example, the arrangement(ABCD) of a city, and the solution is optimized by substitution. In the intermediate solution, the city name of a part allocated to the processor is expressed in B in communication of phase. Since an area with possibility where the city name B exists in the arrangement of an opposite processor 3 is considered as first and second areas, a city name A in addition to its own allocated city name B is sent to the processor 3. Also, the processor 3 sends its own allocated city name D and a fourth city name C. Thereby, symbol information including its own allocated part can be exchanged between the processors 1 and 3, and no duplication and omission of the same symbol occurs in the arrangement, and both the arrangement of the processors 1 and 3 go to the same one(ABCD), which maintains the consistency.