7. Polynomial Fitting

The POLYFIT program creates a polynomial equation (see Appendix A, Section 1) portrayal of data points (independent variable X, dependent variable Y). Such useful representations of related phenomena have the form:

where c, a1, a2, a3, ...an are constants, and the "degree" of the polynomial, n, is at least two less than the number of data points. To run the program, insert the disk into the computer drive bay, set the computer for that drive, and enter POLYFIT. Answer the questions regarding the number of data points and desired degree of the fitting. Then enter the pairs of points, X and Y, separated by a comma. The program gives the values of the constant, the polynomial coefficients, the correlation coefficient, and the standard error of estimate. Also, an opportunity is provided to use the polynomial to determine any Y value for a given X. An example screen is shown below.

For many geomagnetic computations, an extrapolation to future predictions uses a polynomial fitting of the known past behavior. The geomagnetic coordinate computations are extended to ten years past the present using a polynomial fitting of previous main-field Gauss coefficients.

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