The other 3 Operators follow similar logic, and this part is the cornerstone of Goal Stack Planning.
#BLOCK WORLD PROBLEM CODE FREE#
On the other hand, once the operation is performed, The robot arm will be free ( ARMEMPTY) and the block X will be on top of Y ( ON(X,Y)). (Note : It is not necessary for the Precondition and DELETE List to be the exact same). Once the operation is performed, these predicates will cease to be true, thus they are included in DELETE List as well. to Stack Block X on top of Block Y, No other block should be on top of Y (CLEAR(Y)) and the Robot Arm should be holding the Block X ( HOLDING(X)).
Operations performed by the Robot Armįor example, to perform the STACK(X,Y) operation i.e. The Precondition, Add and Delete List for each operation is rather intuitive and have been listed below. ADD List on the other hand contains the predicates which will become true once the operation is performed. DELETE List contains the predicates which will cease to be true once the operation is performed. The effect of these operations is represented using two lists ADD and DELETE. These preconditions are represented in the form of predicates. PICKUP(X) : Picking up Block X which is on top of the tableĪll the four operations have certain preconditions which need to be satisfied to perform the same.UNSTACK(X,Y) : Picking up Block X which is on top of Block Y.STACK(X,Y) : Stacking Block X on Block Y.Thus a configuration can be thought of as a list of predicates describing the current scenario. Goal State - ON(C,A) ∧ ON(B,D) ∧ ONTABLE(A) ∧ ONTABLE(D) ∧ CLEAR(B) ∧ CLEAR(C) ∧ ARMEMPTY Goal State Initial State - ON(B,A) ∧ ONTABLE(A) ∧ ONTABLE(C) ∧ ONTABLE(D) ∧ CLEAR(B) ∧ CLEAR(C) ∧ CLEAR(D) ∧ ARMEMPTY Initial State Using these predicates, we represent the Initial State and the Goal State like this: Given below are the list of predicates as well as their intended meaning Predicates can be thought of as a statement which helps us convey the information about a configuration in Block World.
Representing the configurations as a list of “predicates” World State on the other hand starts off as the Initial State and ends up being transformed into the Goal state.Īt the end of this algorithm we are left with an empty stack and a set of actions which helps us navigate from the Initial State to the World State. Goal Stack uses this world state to work its way from Goal State to Initial State. We make use of a stack to hold these goals that need to be fulfilled as well the actions that we need to perform for the same.Īpart from the “Initial State” and the “Goal State”, we maintain a “World State” configuration as well. We keep solving these “goals” and “sub-goals” until we finally arrive at the Initial State. We start off by fulfilling the preconditions required to achieve the initial state, which in turn have their own set of preconditions. Goal Stack Planning is one of the earliest methods in artificial intelligence in which we work backwards from the goal state to the initial state. Our aim is to c hange the configuration of the blocks from the Initial State to the Goal State, both of which are specified in the diagram above. The robot arm can move only one block at a time, and no other block should be stacked on top of the block which is to be moved. We have a robot arm to pick up or put down the blocks. Some blocks may or may not be stacked on other blocks. There is a table on which some blocks are placed. In this medium article, we will be taking a look at Blocks World Problem and implement Goal Stack Planning to solve the same. Pre-requisites - The course is for any one who has basic understanding of a programming language and data structures, and is ready to learn a new language and build some projects.Goal Stack Planning for Blocks World Problem Implementing Goal Stack Planning for the given configuration of Blocks World Problem Block World Problem - Initial State and Goal State for this article
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