CS 307Assignment, Implementing a Class - Mathematical Matrix

"Linear algebra is a fantastic subject On the one hand it is clean and beautiful. If you have three vectors in 12 dimensional space, you can almost see them."
    - Gilbert Strang, Linear Algebra and its Applications

Programming Assignment 3: Individual Assignment. You must complete this assignment on your own. You may not discuss their work with anyone except the instructor and other members of the instructional staff (TA, section leader, or lab proctor). You may not acquire from any source (e.g., another student or an internet site) a partial or complete solution to a problem or project that has been assigned. You may not show another student your solution to an assignment. You may not have another person (current student, former student, tutor, friend, anyone) “walk you through” how to solve an assignment. Review the class policy on collaboration from the syllabus.

The purposes of this assignment are

  1. To practice implementing a stand alone class.
  2. To work with two dimensional arrays.

Description: Implement a class that represents a mathematical matrix. You are implementing a stand alone class that is a new data type similar to the way we implemented an IntList class in lecture.

Mathematical matrices are used  to solve systems of linear equations. Matrices are used in applications such as physics, engineering, probability and statistics, economics, biology, and computer science. (especially in the area of computer graphics. For example here is a page on how matrices are used to perform rotations on 3d objects in a graphics system. ) 

Matrices appear in the following form:


These matrices represent this system of linear equations:

  x +  5y + 10z + 5w =   4
 6x +  4y + 12z + 4w =   5
10x +  5y + 12z + 11w = 12
 5x + 11y + 23z + 9w  =  7

The above matrix has 4 rows and 4 columns, but the number of rows and columns do not have to be equal. In other words mathematical matrices do not need to be square, but they must be rectangular. Each entry can be an integer or real number. For this assignment you will only deal with matrices of integers. You will implement a class, MathMatrix, that models a mathematical matrix and supports various operations on matrices. See this page for an explanation of the mathematical operations you are implementing. The Wikipedia article may also be useful. After calculus, most students then take a course entitled Matrices and Matrix Calculations.

Provided Files:

  File Responsibility
Implementation MathMatrix.java Provided by me and you. (Okay, mostly you.)
Documentation MathMatrix.html Provided by me.
Implementation Stopwatch.java (For use in experiments) Provided my me
Documentation Stopwatch.html Provided by me
Testing MathMatrixTester.java Provided by me and you
Submission MathMatrix.java and MathMatrixTester.java. Provided by you.

Requirements: The provided source file MathMatrix.java contains a skeleton implementation of a class for modeling mathematical matrices. MathMatrix.java

Implement all of the methods in MathMatrix.java under the constraints of the general requirements.

Experiment: In addition to completing the MathMatrix.java class and adding tests to the MathMatrixTester.java class, perform the following experiments and answer the following questions. Place your results and answers in a comment at the bottom of MathMatrixTester.java.

The code that conducts the experiments is to be included in the MathMatrixTester.java class, but commented out.

Use the Stopwatch class to record the time it takes to perform various operations on MathMatrix objects.

Stopwatch s = new Stopwatch();
//code to time

The Stopwatch class can show the elapsed time in seconds or nanoseconds. See the Stopwatch class documentation for more details.

Experiment 1:

Experiment 2:

Questions. Answer the following questions. Place your answers in your comment at the bottom of MathMatrixTester.java.

  1. Based on the results of experiment 1, how long would you expect the add method to take if you doubled the dimension size of the MathMatrix objects again?

  2. Based on the results of experiment 2, how long would you expect the multiply method to take if you doubled the dimension size of the MathMatrix objects again?

  3. How large a matrix can you create before your program runs out of heap memory? Estimate the amount of memory your program is allocated based on the largest possible matrix object it can create successfully. (Recall, an int in Java takes up 4 bytes.)

  4. The logic of the add and subtract methods of the MathMatrix class are very similar. Code so similar should make you want to generalize it into a method. You are not required to do this on the assignment, but what do you think could be done to generalize the add and subtract methods?

Submission: Fill in the header for MathMatrix.java and MathMatrixTester.java. Replace <NAME> with your name. Note, you are stating, on your honor, that you did the assignment on your own.

When finished use the turnin program to turn in the MathMatrix.java and MathMatrixTester.java files to your cs307 folder.

Checklist: Did you remember to:


  1. Be clear on the difference between MathMatrix objects and the 2d array of ints that serves as the storage container for the ints that make up a MathMatrix object.

    Assume the 2d array of int that is the instance variable for each MathMatrix object is named myCells.

    public MathMatrix add(MathMatrix rightHandSide)
    {   MathMatrix result = new MathMatrix(numRows(), numCols(), 0);
        int valueFromThisMathMatrix = myCells[0][0];
        int valueFromRightHandSide = rightHandSide.myCells[0][0];
        int valueFromResult = result.myCells[0][0];

        // the following line results in syntax error
        // valueFromRightHandSide = rightHandSide[0][0];
  2. Familiarize yourself with the concept of deep copying. (As opposed to shallow copying.) One of the constructors requires you make a deep copy of a 2d array of ints. Implement your copying without using the clone() method. Here is the Wikipedia article on object copying.
  3. If possible use other methods from the MathMatrix class instead of repeating code.
  4. An explanation of the requirements for the toString method.

    In the String that is returned from the toString method the space for each "cell" is equal to the longest value in the matrix plus 1. (Don't forget to consider a minus sign in on of the values.) All cell entries are right justified with newline characters  between rows. For example, given the following MathMatrix.

    10 100 101 -1000
    1000 10 55 4
    1 -1 4 0

    You should return a String that would appear like this. Use newline characters ("\n") to create line breaks.

        10   100   101 -1000
      1000    10    55     4
         1    -1     4     0

    In example above it can be hard to tell how many spaces there are between numbers. In this example the spaces have been replaced by periods to the number of "spaces" is more clearly shown.

    Note, the last line includes a newline character.

    One way of finding the length of an int is to convert it to a String and find the length of the String. Here is an example:

    int x;
    //code to give x a value.
    String s = "" + x;
    int lengthOfInt = s.length();

    //or more simply given an int x
    int lengthOfX = ("" + x).length();

    Doing the toString method using just loops and Strings and if statements is actually a very interesting exercise. Or you can learn how to use the format method from the String class and formatting string syntax. Here is an introduction to formatting String syntax.

  5. The isUpperTriangular method determines if the MathMatrix is an upper triangular matrix. A matrix is upper triangular if it is a square matrix and all values below the main diagonal are 0. The main diagonal is all the cells whose row and column are equal. The values of the elements on the main diagonal don't have to be zero, just the ones below it. A 1 by 1 matrix is always considered upper triangular.

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