Bringing Bart's recent changes into the inequality branch

Including abandonment of agricultural land

src/ac/ed/lurg/country/gams/DietParamCalculationManager.java

@@ -39,10 +39,9 @@ public class DietParamCalculationManager {
 	}
 
 	private double interpolateParam(int year, double initialParam, double shiftParam) {
-		double ratio = (double) (year - ModelConfig.DIET_CHANGE_START_YEAR) /
-				(ModelConfig.DIET_CHANGE_END_YEAR - ModelConfig.DIET_CHANGE_START_YEAR);
-		ratio = Math.min(Math.max(ratio, 0), 1);
-
+		double offset = (ModelConfig.DIET_CHANGE_END_YEAR - ModelConfig.DIET_CHANGE_START_YEAR) / 2.0;
+		double x = year - ModelConfig.DIET_CHANGE_START_YEAR;
+		double ratio = 1 / (1 + Math.exp(-ModelConfig.DIET_CHANGE_RATE * (x - offset))); // sigmoid
 		return ratio * shiftParam + (1 - ratio) * initialParam;
 	}