docs: public static void divideElements(final int j, final int numRows , final double[] u,
                                        final int startU ,
                                        final double realA, final double imagA ) {
  
          double mag2 = realA*realA + imagA*imagA;
  
          int index = (startU+j)*2;
  
          for( int i = j; i < numRows; i++ ) {
              double realU = u[index];
              double imagU = u[index+1];
  
              // u[i+startU] /= u_0;
              u[index++] = (realU*realA + imagU*imagA)/mag2;
              u[index++] = (imagU*realA - realU*imagA)/mag2;
          }
      }