I will go ahead and apologize right away for my general naivete. This is not a homework problem or anything like that, it's a personal project that my limited mathematics knowledge is, well, limiting. I'm not even sure if this is the right sub-section of the forum, so please feel free to re-direct me.

I'm going to try and describe my intention the best that I can, I hope this information is sufficient to answer my question:

I'm trying to find an equation, which I assume will be a function, which results in a set of all points that form a particular shape. The shape is two equilateral triangles, standing "up" and leaning on each other's bases. I did my best to draw a tilted version of it here.

Graphing 3D shapes-img_20100926_135401.jpg

There are four points on the graph that form the boundaries of the shape. The actual numerical values are arbitrary except for their proportions to each other (X,Y,Z): (0,0,0), (5,10,10), (5,-10,10) and (10,0,0)

When X=0, Y and Z=0. For every point that X moves from 0 to 5, there are two points that occur on the Y and Z axis: (Y=2X,-2X and Z=2X). Then from every point that X moves from 5-10, the y/z points are "mirrored" in the opposite direction.

The other way I can think to describe the axis are in comparison to each other:
The X set goes from 0-max linearly. The Y set "expands" outward in a Y^-Y relationship from 0-max halfway through the X set, and then from max-0 in the back half. The Z set is a single set of points from 0-max and max-0.

Once again I excuse myself for general illiteracy in this language, and I would greatly appreciate anyone who would take some time to help me out.