I am attempting to implement in code the math and functions found here:
http://http.developer.nvidia.com/GPUGems/gpugems_ch01.html
So this question is contextual to that article, I'm sorry for that, but I'm trying to make it generalized (edited my Math.SE question) and more accessible.
Before yesterday I didn't know about binormals, but I do understand tangents and normals, but read the binormal is the cross product of tangent and normal vectors. Okay no problem there.
I may be missing some other concept, but just following the above white paper in sequence, I hit a conceptual brick wall at the discussion of the binormal equations.
H(x,y,t) is a function that gives a heightmap of a 2D plane with a linear sine wave given an x and y on the plane and time. It assumes arbitrary internal values, including multiple summed sine waves, to customize the results of the heightmap as time progresses.
Equation 4a
What I'm stuck on is the meaning of the backwards "6" variable. This SE/Math question wouldn't be worth asking, and would be easy to glaze over if the following Equation 4b evaluated each instance of the var, but since it only eval'ed all BUT ONE... I remain stuck.
Equation 4b
My efforts include cross-referencing other binormal equations found on the web and trying to interpret the meaning for coding... but no success.