---
title: "controller"
type: concept
related: [Controller, Alpha Vector, Policy Iteration, Controller Gradient Ascent, Conditional Plan]
source: https://www.jemoka.com/posts/kbhcontroller/
confidence: high
status: active
---

a controller is a that maintains its own state.
constituents \(X\): a set of nodes (hidden, internal states) \(\Psi(a|x)\): probability of taking an action \(\eta(x&rsquo;|x,a,o)\) : transition probability between hidden states requirements Controllers are nice because we:
don&rsquo;t have to maintain a belief over time: we need an initial belief, and then we can create beliefs as we&rsquo;d like without much worry controllers can be made shorter than conditional plans additional information finite state controller A finite state controller has a finite amount of hidden internal state.
Consider the crying baby problem. We will declare two internal state:
\begin{equation} x_1, x_2 \end{equation}
Given our observations and our internal states, we can declare transitions and an action probability \(\Psi\):
We essentially declare a policy vis a vi your observations. It can be a sequence, for instance, if we want to declare a policy whereby if you cry twice then you feed, you can declare:
finite state controller evaluation \begin{equation} U(x, s) = \sum_{a}^{} \Psi(a|x) \qty[R(s,a) + \gamma \qty(\sum_{s&rsquo;}^{} T(s&rsquo;|s,a) \sum_{o}^{} O(o|a, s&rsquo;) \sum_{x&rsquo;}^{} \eta(x&rsquo;|x,a,o) U(x&rsquo;, s&rsquo;)) ] \end{equation}
which is a conditional plan evaluation but we know even litle
and, to construct alpha vectors:
\begin{equation} \alpha_{x} = \qty[U(x, s_1), \dots, U(x, s_{n})] \end{equation}
we just make one alpha vector per node. So the entire plan is represented as usual by \(\Gamma\) a set of alpha vectors. And yes you can alpha vector pruning.
\begin{align} U(x,b) = b^{\top} \alpha_{x} \end{align}
node we want to start at:
\begin{equation} X^{*} = \arg\max_{x} U(x,b) \end{equation}
solving for \(\Psi\) and \(\eta\) policy iteration: incrementally add nodes and evaluate it nonlinear programming: this can be a nonlinear optimization problem controller gradient ascent
