README.md

Modules Modelling Matrices

We define the signature

module type Ring = sig
  type t
  val zero : t
  val one : t
  val add : t -> t -> t
  val mul : t -> t -> t
  val compare : t -> t -> int
  val to_string : t -> string
end

of an algebraic ring structure, where add and mul are the two binary operations on the set of elements of type t. Values zero and one represent the identity elements with respect to addition and multiplication. The function compare establishes a total order on the elements of the set. The auxiliary function to_string is used to generate a string representation of an element. This signature is available in ring/libRing.ml.

Furthermore, a matrix is given by the signature:

module type Matrix = sig
  type elem
  type t
  val create : int -> int -> t
  val identity : int -> t
  val from_rows : elem list list -> t
  val row_count : t -> int
  val col_count : t -> int
  val set : int -> int -> elem -> t -> t
  val get : int -> int -> t -> elem
  val transpose : t -> t
  val add : t -> t -> t
  val mul : t -> t -> t
  val to_string : t -> string
end

Here, elem and t represent the types of the elements of the matrix and the matrix itself, respectively. The functions have the following semantics:

• create n m creates an empty (all zeroes) $n\times m$ matrix.
• identity n creates an $n\times n$ identity matrix.
• row_count m and col_count m return the number of rows and columns in m, respectively.
• from_rows l creates a matrix from the given list of rows (lists of elements). You may assume that l is non-empty and all lists have the same length.
• set r c v m sets the element at row r and column c in matrix m to value v.
• get r c m returns the element at row r and column c from matrix m.
• transpose m returns the transpose of matrix m.
• add a b adds matrices a and b component-wise.
• mul a b computes the matrix multiplication of a and b.
• to_string m produces a string representation of m. Columns shall be separated by single whitespaces and rows by a newline character \n.

This signature is available in matrix/libMatrix.ml.

Perform these tasks:

• IntRing
  In the file intring/libIntRing.ml: Implement a module IntRing that implements the Ring signature for the int type. [0.5 points]
• FloatRing
  In the file floatring/libFloatRing.ml: Implement a module FloatRing that implements the Ring signature for the float type. [0.5 points]
• FiniteRing
  In the file finitering/libFiniteRing.ml: Define a signature FiniteRing that extends the Ring signature with a value elems that represents a list of all elements of the ring's finite set. Make sure that everything in the Ring signature is part of FiniteRing (without copy-pasting them)! [0.5 points]
• BoolRing
  In the file boolring/libBoolRing.ml: Implement a module BoolRing that implements the FiniteRing signature for the bool type. The multiplication in a bool ring is conjunction, the addition is the exclusive or. [0.5 points]
• SetRing
  In the file setring/libSetRing.ml: Implement a functor SetRing that models a ring over the power set of the set in the FiniteRing passed as the functor's argument. SetRing has to implement the Ring signature. We use union and intersection as add and mul operations. The representation produced by to_string is $\left\lbrace e_1,\dots,e_n \right\rbrace$. For compare we use a bit of an unconventional order. First, we order the elements in the set by their own order and then compare the sets lexicographically, e.g. $\emptyset<\left\lbrace 1,2,3 \right\rbrace<\left\lbrace 2 \right\rbrace<\left\lbrace 2,3 \right\rbrace<\left\lbrace 3 \right\rbrace$. The type t in SetRing should be D.t list, if D is the module that is passed to the functor. Make sure that this information about t is exposed to the outside. [1.5 points]
• DenseMatrix
  In the file densematrix/libDenseMatrix.ml: Implement a functor DenseMatrix that satisfies the Matrix signature. The argument of the functor is a Ring that provides everything to implement the matrix operations. The DenseMatrix is supposed to store all elements in the matrix in a list of rows, which are lists of elements. [3 points]
• SparseMatrix
  In the file sparsematrix/libSparseMatrix.ml: Implement a functor SparseMatrix that satisfies the Matrix signature. The argument of the functor is a Ring that provides everything to implement the matrix operations. The SparseMatrix stores only those elements of the matrix that are non-zero. More precisely, the representation of a sparse matrix must have memory usage proportional to the number of non-zero entries in the matrix ( $\mathcal{O}(n)$ ). [3.5 points]

Hint: You may assume that all inputs are valid, e.g. no out-of-bounds access. If you wish to handle invalid input, just throw an exception.

Hint: The function implementations need not be particularly efficient or tail-recursive, just keep your implementations simple where possible.

Assignment Repository Layout and Tests

Testing your solutions is more difficult this week as a test cannot compile if any module it depends on is not correctly implemented or a module signature is incorrectly defined. Thus, we have separated each module into its own dune library (one per directory). This way, we can compile and test each library independently. However, since some tasks require implementations of previous tasks, we have introduced dependencies between the libraries. If building any dependency of a library fails, we cannot test that library (and the corresponding task will receive zero points) as building it would fail too. You can consult the dune files or the graph below to see exactly what the dependencies are. If you don't want to submit a solution for some task, check Artemis to make sure that the public tests for the tasks that you do want to submit pass. In particular, look for the *:build tests, which pass only if that library can be tested and tell you why it cannot otherwise.

Write any code you want to share between tasks in common/common.ml.

To not cause issues with the tests, you should not change the provided dune files (the tests on Artemis will ignore your dune files).

Overview of dependencies

Example: If your implementation of libFiniteRing can't compile, then libBoolRing and libSetRing will not be tested and receive zero points.

Example: You can reuse any implementations you write in libMatrix in libDenseMatrix and libSparseMatrix, but don't change the Matrix signature.

Tip: You can generate similar graphs for any dune project by installing dune-deps with opam install dune-deps, then running e.g. dune-deps | dot -Tpng > deps.png