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/**

* Matrix data-type.

*

* @author Kyler Smith, 2017

*/

public class Matrix {

public static void main(String[] args) {

int[][] data1 = new int[0][0];

int[][] data2 = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};

int[][] data3 = {{1, 4, 7}, {2, 5, 8}, {3, 6, 9}};

Matrix m1 = new Matrix(data1);

Matrix m2 = new Matrix(data2);

Matrix m3 = new Matrix(data3);

System.out.println("m1 --> Rows: " + m1.getRows() + " Columns: " + m1.getColumns());

System.out.println("m2 --> Rows: " + m2.getRows() + " Columns: " + m2.getColumns());

System.out.println("m3 --> Rows: " + m3.getRows() + " Columns: " + m3.getColumns());

//check for reference issues

System.out.println("m2 -->\n" + m2);

data2[1][1] = 101;

System.out.println("m2 -->\n" + m2);

//test equals

System.out.println("m2==null: " + m2.equals(null)); //false

System.out.println("m3==\"MATRIX\": " + m2.equals("MATRIX")); //false

System.out.println("m2==m1: " + m2.equals(m1)); //false

System.out.println("m2==m2: " + m2.equals(m2)); //true

System.out.println("m2==m3: " + m2.equals(m3)); //false

//test operations (valid)

System.out.println("2 * m2:\n" + m2.scale(2));

System.out.println("m2 + m3:\n" + m2.plus(m3));

System.out.println("m2 - m3:\n" + m2.minus(m3));

System.out.println("m2 * m3: \n"+m2.multiply(m3));

}

/**

* Data needs to be a deep copy as not to change the original state.

*/

private int[][] data;

/**

* Constructor for the matrix takes in a 2D array

*

* @param pData

*/

public Matrix(int[][] pData) {

/** Make a deep copy of the data */

if(pData.length != 0) {

int[][] newData = new int[pData.length][pData[0].length];

for(int i = 0; i < pData.length; i++)

for(int j = 0; j < pData[0].length; j++)

newData[i][j] = pData[i][j];

this.data = newData;

} else {

this.data = null;

}

}

/**

* Returns the element specified by the given location

*

* @param x : x cooridinate

* @param y : y cooridinate

* @return int : value at location

*/

public int getElement(int x, int y) {

return data[x][y];

}

/**

* Returns the number of rows in the Matrix

*

* @return rows

*/

public int getRows() {

if(this.data == null)

return 0;

return data.length;

}

/**

* Returns the number of rows in the Matrix

*

* @return columns

*/

public int getColumns() {

if(this.data == null)

return 0;

return data[0].length;

}

/**

* Returns this matrix scaled by a factor. That is, computes sA where s is a

* constant and A is a matrix (this object).

*

* @param scalar : value to scale by

* @return A new matrix scaled by the scalar value

*/

public Matrix scale(int scalar) {

int[][] newData = new int[this.data.length][this.data[0].length];

for (int i = 0; i < this.getRows(); ++i)

for(int j = 0; j < this.getColumns(); ++j)

newData[i][j] = this.data[i][j] * scalar;

return new Matrix(newData);

}

/**

* Adds this matrix to another matrix.

*

* @param other : Matrix to be added

* @return addend

*/

public Matrix plus(Matrix other) throws RuntimeException {

int[][] newData = new int[this.data.length][this.data[0].length];

if(this.getRows() != other.getRows() || this.getColumns() != other.getColumns())

throw new RuntimeException("Not the same size matrix.");

for (int i = 0; i < this.getRows(); ++i)

for(int j = 0; j < this.getColumns(); ++j)

newData[i][j] = this.data[i][j] + other.getElement(i, j);

return new Matrix(newData);

}

/**

* Subtracts this matrix from another matrix.

*

* @param other : Matrix to be subtracted

* @return difference

*/

public Matrix minus(Matrix other) throws RuntimeException {

int[][] newData = new int[this.data.length][this.data[0].length];

if(this.getRows() != other.getRows() || this.getColumns() != other.getColumns())

throw new RuntimeException("Not the same size matrix.");

for (int i = 0; i < this.getRows(); ++i)

for(int j = 0; j < this.getColumns(); ++j)

newData[i][j] = this.data[i][j] - other.getElement(i, j);

return new Matrix(newData);

}

/**

* Multiplies this matrix with another matrix.

*

* @param other : Matrix to be multiplied with

* @return product

*/

public Matrix multiply(Matrix other) throws RuntimeException {

int[][] newData = new int[this.data.length][other.getColumns()];

if(this.getColumns() !=other.getRows())

throw new RuntimeException("The two matrices cannot be multiplied.");

int sum;

for (int i = 0; i < this.getRows(); ++i)

for(int j = 0; j < other.getColumns(); ++j){

sum = 0;

for(int k=0;k<this.getColumns();++k){

sum += this.data[i][k] * other.getElement(k, j);

}

newData[i][j] = sum;

}

return new Matrix(newData);

}

/**

* Checks if the matrix passed is equal to this matrix

*

* @param other : the other matrix

* @return boolean

*/

public boolean equals(Matrix other) {

return this == other;

}

/**

* Returns the Matrix as a String in the following format

*

* [ a b c ] ...

* [ x y z ] ...

* [ i j k ] ...

* ...

*

* @return Matrix as String

* TODO: Work formatting for different digit sizes

*/

public String toString() {

String str = "";

for(int i = 0; i < this.data.length; i++) {

str += "[ ";

for(int j = 0; j < this.data[0].length; j++) {

str += data[i][j];

str += " ";

}

str += "]";

str += "\n";

}

return str;

}

}