code: private static void daxpy(double constant, double vector1[], double vector2[]) {
          if (constant == 0) return;
  
          assert vector1.length == vector2.length;
          for (int i = 0; i < vector1.length; i++) {
              vector2[i] += constant * vector1[i];
          }
      }
docs: constant times a vector plus a vector
  
  <pre>
  vector2 += constant * vector1
  </pre>
  
  @since 1.8