1. An information processing device, comprising: a memory storing instructions; and one or more processors configured to process the instructions to: calculate a mean and a variance of a response variable for each range which is determined based on a partition candidate being information on partitioning a domain of an explanatory variable into a plurality of ranges based on observed data including information representing the explanatory variable and information representing the response variable being an observed value in terms of the explanatory variable and the mean and the variance are dependent on the explanatory variable; select a specific partition candidate among a plurality of the partition candidates by using an information criterion which is calculated based on the observed data and the calculated mean and variance of the response variable; and calculate a smooth function representing the variance of the response variable in the domain of the explanatory variable and a smooth function representing the mean of the response variable in the domain of the explanatory variable based on the mean and the variance calculated for each range determined based on the specific partition candidate.