private double computePhi(DescriptiveStatistics samples, long lastHeartbeat, long currentTime) {
    long size = samples.getN();
    long t = currentTime - lastHeartbeat;
    return (size > 0)
        ? phiFactor * t / samples.getMean()
        : 100;
  }
private double computePhi ( DescriptiveStatistics samples , long lastHeartbeat , long currentTime ) { long size = samples . getN ( ) ; long t = currentTime - lastHeartbeat ; return ( size > 0 ) ? phiFactor * t / samples . getMean ( ) : 100 ; }
Computes the phi value from the given samples.
<p>
The original phi value in Hayashibara's paper is calculated based on a normal distribution.
Here, we calculate it based on an exponential distribution.

@param samples       the samples from which to compute phi
@param lastHeartbeat the last heartbeat
@param currentTime   the current time
@return phi