[10 x 10]=>[30 x 10], interp err = 1.9539e+00
[20 x 20]=>[60 x 20], interp err = 4.3333e-01
[40 x 40]=>[120 x 40], interp err = 8.4606e-02
[80 x 80]=>[240 x 80], interp err = 1.8322e-02