Both seasonal demand r and total demand R in the production inventory model are difficult to estimate precisely to actual r0 and R0 values, respectively. Hence, we will set the membership grade at r0 and R0 in an interval [λ, 1], 0 < λ < 1, and then, obtain the interval-valued fuzzy sets r̃ and R̃, respectively. For each production quantity period q, we can obtain the fuzzy total cost Gq ( r̃, R̃ )...