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interested in state change, then we can only take three variable value +, - and 0
and the equation coefficient is always unit coefficient.
The linear inequality is a kind of widely used constraint. Boolean
combination of constraints is widely used in physical reasoning, circuit design
and planning. Nonlinear equation and inequality are frequently involved in
physical reasoning. In geometry reasoning, algebra and triangular equation are
also involved frequently.
At present, research on constraint reasoning mainly concentrates on two
aspects: constraint search and constraint languages. The main research of
constraint search focuses on constraint satisfaction in definite domain. For
definite domain, constraint satisfaction problem is generally a NP problem. At
present, there are several following methods to solve CSP:
• Backtracking
• Constraint propagation
• Intelligent backtracking and truth maintainance
• Variable order instantiation
• Local revision
Constraint language is another main research aspect for constraint reasoning.
The following is several typical constraint languages:
1. CONSTRAINTS
CONSTRAINTS is a circuit-based constraint representation languages. As a
constraint representation language, CONSTRAINTS uses symbolic technology to
solve mathematical equation. In CONSTRAITS, functions of physical parts and
device structure are represented by constraints, which are generally linear
equation and inequality, and condition expression. Constraint variables are
usually the real variable of the physical quantity, and sometime assigned
dispersed values as well, such as the state of the switch, working state of triode
and so on. The system adopts the expression reasoning and value reasoning, and
realizes dependence-directed backtracking.
One advantage of CONSTRAINTS is to represent constraints at type
hierarchy and adopt constraint to represent function and structure of physical
devices. One constraint's shortcoming is lack of methods which are similar to
object-oriented language, and thus cannot define particular class concept.
Meanwhile, constraint propagate method is monotonous. It lacks interval
