--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/artifacts/src/main/java/org/dive4elements/river/artifacts/math/Linear.java	Thu Apr 25 15:23:37 2013 +0200
@@ -0,0 +1,78 @@
+package org.dive4elements.river.artifacts.math;
+
+public final class Linear
+implements         Function
+{
+    private double m;
+    private double b;
+
+    public Linear(
+        double x1, double x2,
+        double y1, double y2
+    ) {
+        // y1 = m*x1 + b
+        // y2 = m*x2 + b
+        // y2 - y1 = m*(x2 - x1)
+        // m = (y2 - y1)/(x2 - x1) # x2 != x1
+        // b = y1 - m*x1
+
+        if (x1 == x2) {
+            m = 0;
+            b = 0.5*(y1 + y2);
+        }
+        else {
+            m = (y2 - y1)/(x2 - x1);
+            b = y1 - m*x1;
+        }
+    }
+
+    public static final double linear(
+        double x,
+        double x1, double x2,
+        double y1, double y2
+    ) {
+        // y1 = m*x1 + b
+        // y2 = m*x2 + b
+        // y2 - y1 = m*(x2 - x1)
+        // m = (y2 - y1)/(x2 - x1) # x2 != x1
+        // b = y1 - m*x1
+
+        if (x1 == x2) {
+            return 0.5*(y1 + y2);
+        }
+        double m = (y2 - y1)/(x2 - x1);
+        double b = y1 - m*x1;
+        return x*m + b;
+    }
+
+    @Override
+    public double value(double x) {
+        return m*x + b;
+    }
+
+    public static final double factor(double x, double p1, double p2) {
+        // 0 = m*p1 + b <=> b = -m*p1
+        // 1 = m*p2 + b
+        // 1 = m*(p2 - p1)
+        // m = 1/(p2 - p1) # p1 != p2
+        // f(x) = x/(p2-p1) - p1/(p2-p1) <=> (x-p1)/(p2-p1)
+
+        return p1 == p2 ? 0.0 : (x-p1)/(p2-p1);
+    }
+
+    public static final double weight(double factor, double a, double b) {
+        //return (1.0-factor)*a + factor*b;
+        return a + factor*(b-a);
+    }
+
+    public static final void weight(
+        double factor,
+        double [] a, double [] b, double [] c
+    ) {
+        int N = Math.min(Math.min(a.length, b.length), c.length);
+        for (int i = 0; i < N; ++i) {
+            c[i] = weight(factor, a[i], b[i]);
+        }
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :