1 basis[0] = rr * (rr - 1.0) * ss * (ss - 1.0) / 4.0;
2 basis[1] = rr * (rr + 1.0) * ss * (ss - 1.0) / 4.0;
3 basis[2] = rr * (rr + 1.0) * ss * (ss + 1.0) / 4.0;
4 basis[3] = rr * (rr - 1.0) * ss * (ss + 1.0) / 4.0;
6 basis[4] = (1.0 - rr) * (1.0 + rr) * ss * (ss - 1.0) / 2.0;
7 basis[5] = rr * (rr + 1.0) * (1.0 - ss) * (1.0 + ss) / 2.0;
8 basis[6] = (1.0 - rr) * (1.0 + rr) * ss * (ss + 1.0) / 2.0;
9 basis[7] = rr * (rr - 1.0) * (1.0 - ss) * (1.0 + ss) / 2.0;
11 basis[8] = (1.0 - rr) * (1.0 + rr) * (1.0 - ss) * (1.0 + ss);