Smoothed Data Spline Estimation

The Smoothed Data Spline Estimation procedure combines TableCurve 2D's Smoothing and Spline Estimation. Note that this is not a smoothing spline, but is rather the fitting of an interpolating B-spline to data that have been pre-smoothed.

Unless the Loess algorithm is used, uniformly spaced data are needed so that no additional noise is introduced. This procedure does not automatically generate uniform data for the smoothing algorithms. If needed, the Spline Estimation or Local Regression Spline Estimation option can be used to create an interpolated data set with constant X-spacing.

Smoothing Level, AI Expert, and Smoothing Algorithm

These are discussed in the Automated Smoothing option.

B-Spline Order

This is discussed in the Spline Estimation option. Note that the B-Spline will exactly pass through the smoothed data.

Goodness of Fit Statistics

A standard error (SE) and r² are reported. This is based upon the raw data and final spline interpolant. These statistics are of limited use, since a zero smoothing level and B-spline produce a perfect fit of noisy data. They may, however, allow a comparison between a favorable estimation and your choice of a parametric fit.

Output

The principal output will interpolate the spline model or Function. It is also possible to directly evaluate the first or second derivative (1st Deriv, 2nd Deriv).

For derivatives, be very cautious with noisy data. A significant level of smoothing is generally needed to produce accurate derivatives. With noisy data, significant smoothing is essential for valid derivatives. The separate Savitzky-Golay Spline Estimation option is recommended for serious derivative evaluations.

A quadratic spline has a continuous first derivative. A cubic spline is smooth in the first derivative and continuous in the second derivative. A quartic spline is smooth in both first and second derivatives and continuous in the third derivative. If you need a smooth derivative, be sure you use a spline order two greater than the derivative desired.

For the output, the number of elements n are generated between x start and x end. Up to 65536 values can be generated. The starting and ending X values should be at or within the range of the input data. The default values will perform a 2x upsampling within the x range of the data.

List

The List Data option lists the index, time, and output in a three column table. The listing uses the TableCurve 2D text viewer facility.

Copy

The Copy Data to Clipboard option copies the time and output values to the clipboard. Formats include full precision binary (for spreadsheets such as Excel) and ASCII (for pasting into text editors).

Save

The Save Data to Disk option writes the time and output values to a supported file format. These formats include ASCII, Excel 97/2000, Excel 95, Lotus WK3, Lotus WK1, SPSS, or Systat.

Production Facility

The TableCurve 2D Automation facility allows unattended processing of large numbers of data sets. The data sets can be consolidated in an Excel file or acquired using a DLL. The graphs can be exported to an MS Word/RTF file, while the processed data can be exported to an Excel 95 or Excel 97/2000 file.

The Reset button restores the data to its state when first entering the procedure. If an Automation Session is in progress, the Reset button can be used to terminate the automated processing.

Residuals

The Residuals button opens a TableCurve 2D Graph containing the residuals from the spline fit. The residuals are the difference between the data and spline model. This option is not available for the spline procedures that exactly interpolate the data.

Evaluation

The Evaluation option offers the means to more extensively evaluate the spline model. The evaluation can be be direct, or the computation can consist of first or second derivatives, roots, or integrated areas. This option can be used to generate a table or file of any size using a generated X grid or by importing X data from supported file formats.

MS Word/RTF Export

The MS Word/RTF File Export option is used to save the current graphs to either an MS Word file or a portable RTF (Rich Text Format) file. The graph is inserted into the file as a Windows metafile.

Automatic Update

The List, Residuals, and Evaluation windows are automatically updated when any change is made to the algorithm's settings.

Updating the Data Table

When exiting this procedure with the OK button, an option will be presented to update TableCurve 2D's main data table with the estimated data.

If Background Thread Fitting is active, the fitting will be initiated as soon as the estimation is accepted and the data is rescanned.