Problem Detail: The state space is decribed with 3 boolean variables $p,q$ and $r$ (so we have 8 states total). We have an action, let’s say $a$. Action $a$ can be executed when $p=text{False}$ and $q=text{True}$ and the result is $p=text{True}$, $q=text{False}$ and $r=text{False}$ How can we describe this action with STRIPS? My problem is this: since it isn’t allowed on STRIPS to have negative literals, how can I describe it? For example, $text{precondition}(a) = { neg p,q }$.
Asked By : Adasel Pomik
Answered By : Vor
An instance of propositional STRIPS planning is a quadruple $langle P,O,I,G rangle$
- $P$ is the set of atomic ground formulas;
- $O$ is the set of operators (actions); an operator $a in O$ has the form $Pre Rightarrow Post$, where $Pre$ is a satisfiable conjuction of positive ($a^+$) and negative preconditions ($a^-$) of the operator; $Post$ is a satisfiable conjunction of positive ($a_+$) and negative ($a_-$) postconditions of the operator ($a_+$ is called the add list, $a_-$ is called the delete list);
- $I subseteq P$ is the initial state;
- $G = langle G_+, G_- rangle$, called the goals, is a satisfiable conjunction of positive and negative conjunctions;
- the state $S$ is a subset of $P$.
The result of applying operator (action) $a$ on state $S$ is:
- $(S cup a_+) setminus a_-quad$ if $a^+ subseteq S$ and $S cap a^- = emptyset$
- $S$ otherwise
In your example simply set: $$a^+ = {q}, quad a^- = {p}$$ $$a_+ = {p}, quad a_- = {q,r}$$ For a formal definition and a nice computational complexity characterizations of STRIPS with various constraints on the preconditions/postconditions see: The Computational Complexity of Propositional STRIPS Planning (1994), by Tom Bylander.
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Question Source : http://cs.stackexchange.com/questions/14066
