.NET Opensource

I came across Math.NET when searching for a simple linear interpolator in c#.  It seems an elegant and useful solution,  I would like to use it, but have a small problem, perhaps somebody can help.

I have an application in which I need to do 1-d interpolation with an unknown number of points, between 3 and 7, the number will vary.

The default method (barycentric) seems to fail with only 3 points.

            double[ values = new double[ { 6.0, 12.0, 16.0 };
            double[ points = new double[ { 1.0, 2.0, 3.0 };
            IInterpolationMethod method = Interpolation.Create(points,values); // t, x);
            IInterpolationMethod method2 = Interpolation.CreatePolynomial(points, values);

            double a = method.Interpolate(2.5);

            double b = method2.Interpolate(2.5);

 a gives NaN, b gives 14.25

 CreatePolynomial works, but I would prefer linear interpolation between the closest points, to return value of 14.0.  I do not see an obvious linear interpolation example.  Can anyone advise me as to the best approach for using Math.Net with only 3 values, advise as to what would come closest to linear interpolation, and point me to a relatively simple explanation of the various  interpolants that are supported.

 Thanks in advance.

 Richard Males

Cincinnati, OH USA

Thanks for reporting, there is indeed an issue with barycentric interpolation when the number of provided samples are exactly equal to the interpolation order (3 in this case).

Luckily, since what you really want is linear interpolation, you should use CreateLinearSpline instead, which works fine for your 3 samples and does indeed return 14.0 at 2.5.

Thank you for the response, I discovered and have been using the CreateLinearSpline successfully.