Interpolating a Value from a Data Set

The Interpolation page uses the polynomial interpolation function to interpolate (or extrapolate) values given a set of known data points that you provide.

The QSR attempts to fit a polynomial to the given data points. The polynomial is of the (i - 1) order, where i is the number of data points. You must enter at least 2 data points, and you cannot enter more than 10.

Note that if the given data points are far from the point of interest, the resulting polynomial can oscillate between values, thus yielding erroneous results. Moreover, interpolation based on only data points, with no background information on the actual function, can also yield erroneous results. For these reasons, an approximate error value is returned with each interpolation.

Follow the steps outlined below to obtain values with the QSR:

• In the Input area of the Interpolation page, specify the number of data points you wish to enter in the Number of x-y Values field. Then click the Update button to create a table on the left of the page where you can enter the known data points that you wish to interpolate from.
• In the table on the left side of the page, enter the x- and y-values data points that you wish to interpolate from.
• In the Input area, enter the x-value for which the corresponding y-value will be obtained.
• Click the Calculate button to obtain the corresponding y-value of the x-value you entered in the Input area. The y-value and an approximate error value are displayed in the Output area.