Inflation is the rise in prices of those, fundamental need of society. The occurrence of inflation can be measured by the consumer price index (CPI). The increase in inflation was due to several expenditures based on people’s needs. If inflation is high, it can affect competitiveness in the sectors of the industry. The purpose of this study is to compare functions describing the movement of inflation data in West Java using Newton-Gregory Forward Interpolation Method and the Cubic Spline Interpolation Method. Based on the results of the study, it is found that both methods result in smooth functions. However, in the Cubic Spline Interpolation Method there is no significant change in the value of the function/data within each subinterval. Meanwhile, in Newton-Gregory Forward Interpolation, there are significant changes in the value of the function/data between the ends of the right-hand side subintervals. This implies that errors of the function produced by Cubic Spline interpolation are less than those of the other one. Therefore, the Cubic Spline Interpolation Method is better than Newton-Gregory in predicting the inflation percentage data in West Java.
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