Regression (TI 86)

Goal: We wish to determine a "closest" function of a given form to the points represented by a list of ordered pairs (the data points).

Preliminaries:We will proceed with an example that finds the best fit to our data points in the form of a 3rd degree polynomial.

Assume that the data is represented in two lists. The first list, L1, contains the x-coordinates (in order) of our data points and the second list, L2, contains the y-coordinates.

Step by step method:

• STAT/EDIT
• Move the cursor (with arrow keys) to the heading of a vacant column. Enter L1 as the x-list name. In a second column, enter L2 as the y-list name.
• Move to the first entry under the x-list name and enter the x-coordinates down this column. Fill the y-list in a similar manner. EXIT
• STAT/CALC Choose P3Reg followed by the x-list and y-list names (comma separated)
• Produced, is a list named PRegC containing the coefficients of the regression ploynomial listed from the coeff of x^3 downward
• To put the regression polynomial in y1, enter the "y(x)=" menu, place cursor after \y1= and enter RegEq (found under STAT/VARS ) or type in PRegC(1)x^3+PRegC(2)x^2+PRegC(3)x+PRegC(4).

Remark: Other function forms are available at the point where P3Reg is chosen.

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