text: /**
   * Copyright (C) 2011 Brian Ferris <bdferris@onebusaway.org>
   *
   * 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 org.onebusaway.transit_data_federation.impl.probability;
  
  import cern.jet.stat.Probability;
  
  public class HalfNormal {
  
    private static final double SQRT_TWO = Math.sqrt(2.0);
  
    private final double _sigma;
  
    public HalfNormal(double sigma) {
      _sigma = sigma;
    }
  
    public double cdf(double x) {
      if (x < 0)
        return 0.0;
      return Probability.errorFunction(x / (SQRT_TWO * _sigma));
    }
  }
  