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Matrix Class - 3 X 3 Matrices
This simple class has:
(1) an operator function to overload the * symbol to perform multiplication
of a matrix by a scalar. For example,
| 1 1 1 |
| 2 2 2 |
| 2 2 2 | times 2.0 gives | 4 4 4 |
| 3 3 3 |
| 6 6 6 |
This will work using the statement:
mat2 = mat1*alpha;
However, in mat_driver.cpp, the statement
mat2 = alpha*mat1;
will not work. Why?
Here's a friend function that will work for alpha*mat1 :
Matrix operator*( double alpha, Matrix& Z )
{
Matrix temp;
for(int i=0; i < 3; i++)
for(int j=0; j < 3; j++)
temp.M[i][j] = alpha * Z.M[i][j];
return temp;
}
Remember to put the declaration in the Matrix.h file:
friend Matrix operator*( double, Matrix& );
(2) a friend function to create the transpose of a matrix. The transpose
switches the rows and columns. For example, the transpose of
| 1 1 1 | | 1 2 3 |
| 2 2 2 | is | 1 2 3 |
| 3 3 3 | | 1 2 3 |
Class Declaration
% cat Matrix.h
// Class declaration
class Matrix
{
private:
double M[3][3];
public:
Matrix(); // constructor
Matrix operator*( double ); // operator*
function
// matrix*scalar
// non-member friend functions
friend Matrix transpose( Matrix & );
friend istream& operator>>(istream&, Matrix&
);
friend ostream& operator<<(ostream&, Matrix&
);
// for scalar*matrix
friend Matrix operator*(double alpha, Matrix& Z);
};
Class Implementation
% cat Matrix.cpp
#include<iostream>
using namespace std;
#include <iomanip>
#include "Matrix.h"
// implementation section
// constructor
Matrix::Matrix()
{
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
M[i][j] = 0.0;
}
// operator functions
Matrix Matrix::operator*( double alpha )
{
Matrix temp;
for(int i=0; i < 3; i++)
for(int j=0; j < 3; j++)
temp.M[i][j] = alpha*M[i][j];
return temp;
}
// non-member functions
ostream& operator<<(ostream& out, Matrix& q)
{
for(int i=0; i < 3; i++)
{
for(int j=0; j < 3; j++)
out << q.M[i][j]
<< " ";
cout << endl;
}
return out;
}
istream& operator>>(istream& in, Matrix& q)
{
for(int i=0; i < 3; i++)
for(int j=0; j < 3; j++)
in >> q.M[i][j];
return in;
}
Matrix transpose( Matrix &Q )
{
Matrix temp;
for(int i=0; i < 3; i++)
for (int j=0; j < 3 ; j++)
temp.M[j][i] = Q.M[i][j];
return temp;
}
// friend for scalar*matrix
Matrix operator*(double alpha, Matrix &Z)
{
Matrix temp;
for(int i=0; i < 3; i++)
for (int j=0; j < 3 ; j++)
temp.M[i][j] = alpha*Z.M[i][j];
return temp;
}
Data File
% cat matA
1 1 1
2 2 2
3 3 3
Driver Program & Execuation
% cat mat_driver.cpp
// driver program to test Matrix class
#include<iostream>
using namespace std;
#include <fstream>
#include "Matrix.h"
int main()
{
char dataFile[21];
ifstream file1, file2;
Matrix mat1, mat2, mat3, mat4;
cout << "Enter name of data file for matrix A: ";
cin >> dataFile;
file1.open(dataFile);
file1 >> mat1;
cout << mat1;
cout << "\nScalar multiple" << endl;
double alpha = 2.0;
cout << "Use member operator function" << endl;
mat2 = mat1*alpha;
cout << mat2;
cout << "\n\nUse friend operator function" <<
endl;
mat3 = alpha*mat1
cout << mat3;
cout << "\nTranspose" << endl;
mat4 = transpose( mat1 ); // friend function
cout << mat4;
}
% g++ mat_driver.cpp Matrix.cpp
% a.out
Enter name of data file for matrix A: matA
1 1 1
2 2 2
3 3 3
Scalar multiple
Use member operator function
2 2 2
4 4 4
6 6 6
Use friend operator function
2 2 2
4 4 4
6 6 6
Transpose
1 2 3
1 2 3
1 2 3
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