Quality of interpolation: average difference from f(x)
                      polinomial order of interpolation
      spline         1st         3rd         5th         7th
1.    0.0526      0.1410      0.0848      0.1434      0.2808
2.    0.0004      0.0171      0.0013      0.0012      0.0004
3.    0.0171      0.0205      0.0162      0.0295      0.0749