docs: static public double[] regres(Vec xData, Vec yData)
      {
          //find y = a + B *x
          double[] toReturn = new double[2];
  
          //B value
          toReturn[1] = DescriptiveStatistics.sampleCorCoeff(xData, yData)*yData.standardDeviation()/xData.standardDeviation();
          //a value
          toReturn[0] = yData.mean() - toReturn[1]*xData.mean();
  
          return toReturn;
      }