TrendEstimator.java

/*******************************************************************************
 * Copyright 2012 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/
package emlab.gen.util;


import org.apache.commons.math.stat.regression.SimpleRegression;

public class TrendEstimator {

    
    public static double[] estimateLinearTrend(double[][] input, double[] predictionYears){
        ;
        //Get logarithm of second trend
        SimpleRegression sr = new SimpleRegression();
        sr.addData(input);
        double result[] = new double[predictionYears.length];
        for(int i = 0 ; i<result.length; i++){
            result[i]=sr.predict(predictionYears[i]);
        }
        return result;
        
    }
    
    
    public static double[] estimateGeometricTrend(double[][] input, double[] predictionYears){
        //Get logarithm of second trend
        for(int i=0;i<input.length;i++){
            input[i][1]=Math.log(input[i][1]);
        }
        //input[1]=log;
        SimpleRegression sr = new SimpleRegression();
        sr.addData(input);
        double result[] = new double[predictionYears.length];
        for(int i = 0 ; i<result.length; i++){
            result[i]=Math.exp(sr.predict(predictionYears[i]));
        }
        return result;
        
    }

}