README.md

Overview

This is a java library for using concepts and constructions from abstract algebra. It is focused on providing code that closely matches the way an algebraist would define things, and providing a framework for checking the implementations for correctness.

For example, a mathematical (abelian) group is a set coupled with an operation plus that is commutative, associative, has an identity element and an inverse. This is exactly how to read the code for algebra.concept.Group:

interface Group<E> extends Set<E> {
	@Commutative @Associative @Identity("zero") @Inverse("neg")
	E plus (E, E);

	E zero ();

	E neg (E e);
}

The key feature here are the annotations @Commutative, @Associative, etc. They are each given executable definitions that can be tested. For example, a binary function f from E x E to R is commutative if f(a,b) equals f(b,a). This is captured by the code for @Commutative (in algebra.properties):

@interface Commutative {

	...
	boolean check(Binary<E,E,R> f, Binary<R,R,Boolean> eq, E a, E b)
	{
		return eq.ap(f.ap(a,b), f.ap(b,a));
	}
}

This framework is supported by a custom annotation processor (in the processor/ directory). This processor ensures that methods annotated with these properties are correctly typed (for example, @Commutative E zero() is nonsense because zero is not a binary relation), and also generates randomized tests that invoke the property definitions.

Source Code

The source code for library is contained in the src/ directory; the processor/ directory contains the annotation processor mentioned above.

The com.mdgeorge.geometry package contains geometric constructions that make use of the com.mdgeorge.algebra classes. They can serve as an example of how to use the library. The algebra package contains the meat of the library:

• com.mdgeorge.concept contains interfaces defining the algebraic concepts: Group, Ring, Module, etc.
• com.mdgeorge.properties contains annotation classes that define properties of methods, such as @Commutative, @Associative, etc.
• com.mdgeorge.construction contains number types that instantiate the algebraic concepts. Some, such as Z (the integers), Q (the rationals) and Float are used to handle Java's built in numbers. Others (such as FieldOfFractions) can be parameterized by another number type.
• com.mdgeorge.adapter contains utility classes that wrap number types and add useful methods. For example, the OrderedField interface provides an inverse method, but not a division method. OrderedFieldUtils wraps an OrderedField and adds a division method. It also adapts the OrderedField to the java.util.Comparator interface, since the two types are equivalent but defined differently.

Building

Just run ant in the top directory.