This block computes
y = a1 + a2 x1 + a3 x12 + a4 x2 + a5 x22 + a6 x1 x2 + a7 x1^3 + a8 x2^3 + a9 x12 x2 + a10 x1 x22
.BuildingSystems.Utilities.Math.Bicubic .BuildingSystems.Utilities.Math.Bicubic