Polynomial Regression
polynomial regression where x = day, y = cost
polynomial regression degrees 2-4
Method
The polynomial regression can be generated by the RDOUBLE formula below.
The function in the example below is for a polynomial regression of the third degree.
If you require a function of a different degree, simply edit the 3 in the poly function to whichever degree you need.
Formulation
To keep this approach generalized, I did not convert the values to a time series (ts). Instead, I used the rank function to convert each x-axis element to a vector of 1-n by using the RANK function.
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