code: public static void Forward(double[] data) {
  
          double[] result = new double[data.length];
          double sum;
          double scale = Math.sqrt(2.0 / data.length);
          for (int f = 0; f < data.length; f++) {
              sum = 0;
              for (int t = 0; t < data.length; t++) {
                  double cos = Math.cos(((2.0 * t + 1.0) * f * Math.PI) / (2.0 * data.length));
                  sum += data[t] * cos * alpha(f);
              }
              result[f] = scale * sum;
          }
          for (int i = 0; i < data.length; i++) {
              data[i] = result[i];
          }
      }
docs: 1-D Forward Discrete Cosine Transform.
  
  @param data Data.