NonUniformInterpolation.java

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package theba.core.math;

public class NonUniformInterpolation {

        double[] samples;

        double[] values;

        public NonUniformInterpolation(double[] invals, double[] outvals) {
                if (invals.length != outvals.length)
                        throw new RuntimeException("Lengths must be equal!");
                samples = invals;
                values = outvals;
        }

        public double interpolate(double val) {
                double result;
                int next = 0;
                int prev = 0;
                int i = 0;
                for (i = 0; i < samples.length; i++) {
                        prev = next;
                        next = i;
                        if (samples[next] > val)
                                break;
                }

                // we probably should extrapolatevalues if outside table-lengthm
                // but currently we just ignore them
                if (i == samples.length - 1) {
                }
                double diff = samples[next] - samples[prev];
                double d = (samples[next] - val) / diff;
                result = values[next] * (1.0 - d) + values[prev] * d;

                return result;
        }

        public static void main(String[] args) {
                double[] samplepoints = { 0.0, 0.5, 1.0, 1.5, 2.0, 2.5 };

                double[] xvalues = { 0, 1, 2, 3, 4, 5, 6 };
                double[] yvalues = { 0, 1, 1, 3, 3, 5, 6 };

                NonUniformInterpolation nx = new NonUniformInterpolation(samplepoints,
                                xvalues);
                NonUniformInterpolation ny = new NonUniformInterpolation(samplepoints,
                                yvalues);

                System.out.println("x" + nx.interpolate(1.25));
                System.out.println("y" + ny.interpolate(1.25));

        }
}