code: public void apply(Vector x, int i1, int i2) {
          double temp = c * x.get(i1) + s * x.get(i2);
          x.set(i2, -s * x.get(i1) + c * x.get(i2));
          x.set(i1, temp);
      }
docs: Applies the Givens rotation to two elements of a vector
  
  @param x
  Vector to apply to
  @param i1
  Index of first element
  @param i2
  Index of second element