对于 custom gate 约束的理解

[Demian101]

如下是一个 Fibonacci 的加法门：

        meta.create_gate("add", |meta| {
            //
            // advice | selector
            //   a    |   s
            //   b    |
            //   c    |
            //
            let s = meta.query_selector(selector);
            let a = meta.query_advice(advice, Rotation::cur());
            let b = meta.query_advice(advice, Rotation::next());
            let c = meta.query_advice(advice, Rotation(2));
            vec![s * (a + b - c)]
        });

我的问题在于 —— 是不是说，对于所有 query_selector(selector); 的结果， 每当 query 到选择器为 1 的情况时，都会对“区域” 进行这套 custom 的约束检查 。

比如有 100 个 s 都是 1 ，那就依据这 100 个 s 的位置，撑（或者说模拟出）出 100 个 region 来进行这套检查。

• "区域" 就是以 selector 的位置为基准, 然后让 Rotation::cur() / Rotation::next() / Rotation(2) 来 "撑起" 这个区域。
• 就像推箱子一样，每向下推一步，活动区域就大一格。
• Rotation(1) -> Rotation(2) 就相当于把 region 向下撑大了一格

所以，我们就不需要在 meta.custom gate 这里写循环（我之前一直疑惑这个问题），我们唯一需要在 custom gate 这里做的，就是构造最小的约束逻辑单元：

所以说，我在写 assign 给电路赋值的时候，每当要给一个 Selector 赋值为 1 ，都要清晰地认识到：未来在电路 synthesize() 的时候，依据 custom gate 里的约束，这里都会有一个门贴合过来，去检查以 selector 为基准的这个门里覆盖到的所有 cell & region (是否满足定义的约束)

[LiuJiazheng]

Since the original description using analogy, I am not I am not 100% I understood it.
Based on my understanding, I would say that I got same ‘feeling’. The examination you could do here is to check what on earth Rotation is. In fact, Rotation gives you a relative row indicator and it is implemented by +1/0/-1. And from its implementation you can easily derive that, it is describing a relative relationship, or say, recursion.
In a Region, all recursive relationships are enforced.
So the recursive relationship you defined determines a basic shape on the region.
Just like Tetris( sorry using analogy as well)

[LiuJiazheng]

But region size (row number) would be adjusted for a size suitable for FFT. Most of time it would be larger than what you thought.