1. An information processing apparatus for prediction of system outputs, comprising: a memory; and a processor coupled to the memory and configured to: generate a first fitting curve represented by a sum of exponential functions for a set of first digital inputs measured by a first sensor and a second fitting curve represented by a sum of exponential functions for a set of first digital outputs measured by a second sensor, for a physical system that is represented by one or a plurality of equations including m-order differential operators, wherein m is an integer equal to or greater than 1; calculate coefficients of the differential operators, which are included in first coefficients, so that a first coefficient of each exponential function included in an expression obtained by a product of the differential operators and the first fitting curve for the set of the first digital inputs is equal to a second coefficient of a same exponential function, which is included in the second fitting curve for the set of the first digital outputs; and predict second digital outputs of the physical system based on an output function obtained from the second fitting curve and coefficients of the output function, which are calculated from the coefficients of the differential operators and second digital inputs of the physical system.