Having input a number of known X,Y points on a curve, these programs will compute the Y coordinate of a point on the curve given the X coordinate.  Interpolation means finding a point on a curve that has been defined by a number of points. You cannot go beyond the known endpoints of the curve.  If you want to go beyond the endpoints, of a defined curve, that is extrapolation, and you find the programs to do that in the regression section.

Additional programs were contributed for this section, and can be found here,

Interesting links:

http://www.wam.umd.edu/~petersd/interp.html

A java applet that compares interpolation types.

 http://mss.math.vanderbilt.edu/cgi-bin/MSSAgent/~pscrooke/MSS/fitpoly.def

Very cool polynomial fitter!

http://www.oslo.sintef.no/NAM/people/xic/spline_demo/

Demo program for cubic spline interpolation.