Cubic splines

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What is a cubic spline?

A cubic spline is defined as a piecewise function of polynomials of degree 3. Cubic splines are used in interpolation problems where they are preferred to usual polynomial interpolation methods. The reason being that they allow a compromise between the smoothness of the curve and the degree of the polynomial.

Use of the cubic splines in XLSTAT

Cubic splines are defined from a set of nodes. In XLSTAT, three options are offered:

  • Use data as nodes
  • Define a number of nodes equally distributed.
  • Choose a set of nodes

Results for the cubic splines in XLSTAT

  • Coefficients of the polynomials: This table displays the coefficients of polynomials of degree 3 of the cubic spline.
  • Prédictions and residuals: For each observation, the value of the dependent variable, the predictions, the residuals and the standardized residuals are displayed.
  • Spline curve: The cubic spline and the selected nodes are displayed.

XLSTAT

This analysis is available in the XLStat-Base addin for Microsoft Excel

About KCS

Kovach Computing Services (KCS) was founded in 1993 by Dr. Warren Kovach. The company specializes in the development and marketing of inexpensive and easy-to-use statistical software for scientists, as well as in data analysis consulting.

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