docs: public float[] t2(float[] z, int k) {
      float[] result = new float[z.length];
  
      System.arraycopy(z, 0, result, 0, k);
  
      int l = z.length - k;
      for (int i = k + 1; i <= k + l / 2; i++) {
        int head = k + 2 * (i - k) - 1;
        int tail = k + 2 * (i - k);
        float[] subZ = subVector(z, head - 1, tail - 1);
  
        result[i - 1] = (new Transformations()).rNonsep(subZ, 2);
      }
      return result;
    }