/* Function to find the mean value in a vector<double>.

   Receive: vec, a nonempty vector<double>
   Return:  the mean of the values in vec
   Note:    Must #include <numeric> to use accumulate()
----------------------------------------------------------*/

double mean(const vector<double> & vec)
{
  if ( vec.empty() )
  {
    cerr << "\n***mean(vector): vector is empty!" << endl;
    return 0.0;
  }
  else
    return accumulate(vec.begin(), vec.end(), 0.0) / vec.size();
}