Thank you! I suppose what I don't grasp is while single point evaluation can happen at any float x, y, z position, how is the number and location of points determined when performing binary operations?

For example, in $3 = $1 + $2 in the ArrayEvaluator :

To perform the addition, it appears that some sampling has to happen, since an operation a+b amonts to matrix/vector addition considering
#define a v.row(a_).head(count_simd)
#define b v.row(b_).head(count_simd)

With $2 = 2.0 being a constant in this case, the sampling question seems to fall upon $1. With X() initially defined as a free variable, how the is conversion from a free variable to a vector/sampled values handled? A libfive interval or region could be defined that provides bounds, but is single point evaluation performed in between?

Okay, I think I see the issue here – the code that you pasted allows us to evaluate multiple XYZ points in a single pass, which is an optimization, but is misleading if you're just trying to understand the basic evaluation procedure for a single XYZ point.

Before the evaluation loop, XYZ positions are loaded into an array v with the set function.

If you're evaluating a single point, you would call ArrayEvaluator::value({x, y, z}). This would call set to load that point into the 0th slot in the data array, then ask for only one sample when evaluating here.

If you want to sample, then you could load multiple values by calling

ArrayEvaluator a = ...;
a.set({x0, y0, z0}, 0);
a.set({x1, y1, x1}, 1);
...

Then you'd call a.values(NUMBER_OF_VALUES) and it would return the array of results for all of your values.

In other words, the ArrayEvaluator is very dumb and will only run on XYZ point data that you've already loaded; if you want to do any sampling, you have to handle it yourself.

Thank you!!