All, I've completed MATH-1138 ( BicubicSplineInterpolator is returning incorrect interpolated values ). It is generating substantially better values. I am using the Akima Spline algorithm that I added to the library (with unit tests). For the planar test the error off the truth function went from 6 to 6e-14. On the parabaloid function test it went from 224 to 6e-14. The corresponding errors on the Akima Spline test for linear, parabolic and cubic functions are 1e-15, 6e-14 and 3.8, respectively. While that is an improvement over the Natural Spline, that could have errors over 15 on the cubic test, the B-spline would collapse errors on the higher order functions to something comparable to the linear and parabolic tests, and thus further enhance the accuracy of the interpolation of the higher dimension interpolators too. However that should probably be another story as well since this answers the mail on the heart of the MATH-1138 problem.
The TricubicSplineInterpolator needs fixing as well. The unit tests weren't actually running any accuracy tests. I would like to recode the Tricubic spline interpolator using the same piecewise methodology that I used on the BicubicSplineInterpolator. I would also like to update the unit tests so that they are performing the accuracy checks as well. So, the stories I would like to add to the Math Wish List and corresponding JIRA stories would be: 1. Add a sense of caching of interpolation functions for BicubicSplineInterpolator for bands that have already had the test function built. 2. Upgrade TricubicSplineInterpolator to achieve appropriate numerical accuracies and round out unit tests 3. Add a B-spline interpolator, with appropriate unit tests 4. Upgrade the BicubicSplineInterpolator to allow the user to select between interpolation methods (Natural, Akima and B-Spline) 5. Create a BiLinearInterpolator Is that amenable with everyone? Hank