I am writing a n by m matrix class which includes overloading multiplications. At the moment code works for n by n matrices and n by m multiplication only if the columns of the first input matrix matches up with the rows of the second matrix, not the other way around. So for example:
a1 a2 * b1
b2
This would work (Sorry I don't have enough reputation points to post images but think of this as a 1x2 matrix * 2x1 matrix).
a1 *b1 b2
a2
But this type of input does not work. The my matrix class is given by:
#include<iostream>
#include <stdlib.h>
using namespace std;
class dymatrix
{
friend ostream & operator << (ostream &os, const dymatrix &om);
friend istream & operator >> (istream &is, dymatrix &om);
private:
int rows;
int columns;
double *matrix;
public:
dymatrix(){cout<<"Default constructor called"<<endl; columns = 0; rows=0; matrix=0;}
~dymatrix(){cout<<"Destructor called"<<endl;delete[] matrix;}
dymatrix(int inrows, int incolumns) //Parametrised objects, matrix database is defined here to store data.
{
rows = inrows;
columns = incolumns;
matrix = new double [inrows*incolumns];
for (int i=0; i<inrows*incolumns; i++)
{
matrix[i]=0;
}
}
int lengthr() const {return rows;} //Returns number of rows.
int lengthc() const {return columns;} //Return number of columns.
dymatrix &operator=( dymatrix &arr); //This is the assignment member function.
dymatrix(dymatrix&); //This is the deep copy member function.
dymatrix operator*(const dymatrix& arr)const ; //Overloading "*" operator.
double & operator[](const int n) //Overloading "[]" operator, this is important !!!
{
if(n<0 || n>=rows*columns)
{
cout<<"Error: trying to access matrix element out of bounds"<<endl;
exit(1);
}
return matrix[n];
}
int index(int j, int i) const //This member function returns the position of each index.
{
if (j > 0 && j <=rows && i > 0 && i <=columns)
{
//cout<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl;
return (i-1)+(j-1)*columns;
}
else {cout<<"Error, out of range"<<endl<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl; exit (1);}
}
double & operator()(int j, int i) const {return matrix[index(j,i)];} //The operator () returns the position of j and i in 1D array.
}; //Class End.
Where the "index" member function returns the location of each element inside the matrix into a 1D array:
int index(int j, int i) const //This member function returns the position of each index.
{
if (j > 0 && j <=rows && i > 0 && i <=columns)
{
//cout<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl;
return (i-1)+(j-1)*columns;
}
else {cout<<"Error, out of range"<<endl<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl; exit (1);}
}
double & operator()(int j, int i) const {return matrix[index(j,i)];} //The operator () returns the position of j and i in 1D array.
This is the part where I overload the multiplication " * " operator outside my class:
dymatrix dymatrix:: operator * (const dymatrix &arr) const //Overloading "*" operator.
{
if (columns != arr.rows)
{
cerr<<"SIZE DO NOT MATCH, YOU FAIL"<<endl; exit(1);
}
dymatrix new_matrix(rows,arr.columns);
for (int j = 1; j <= rows; j++)
{
for (int i = 1; i <= arr.columns; i++)
{
for (int k = 1; k <= columns; k++)
{
new_matrix.matrix[index(j,i)]= new_matrix.matrix[index(j,i)]+ matrix[index(j,k)]*arr(k,i);
cout<<"new_matrix = "<<new_matrix<<endl<<endl;
}
}
}
return new_matrix;
}
And the int main is given here:
int main()
{
dymatrix a1;
cin >> a1; //Define the rows of the matrix
cout << a1<<endl<<endl;
dymatrix a2;
cin >> a2;
cout << a2<<endl<<endl;
dymatrix resu_a3;
resu_a3 = a1*a2;
cout<<"Multiplication = "<<resu_a3<<endl;
return 0;
}
So the error message I get after ran the code is the one which I wrote myself in the "index" member function:
"Error, out of range".
This error message suggests that i and j are either less than 0 or greater than number of existing columns and rows respectively, which I do not understand why that would be the case.
My full code is given here:
#include<iostream>
#include <stdlib.h>
using namespace std;
class dymatrix
{
friend ostream & operator << (ostream &os, const dymatrix &om);
friend istream & operator >> (istream &is, dymatrix &om);
private:
int rows;
int columns;
double *matrix;
public:
dymatrix(){cout<<"Default constructor called"<<endl; columns = 0; rows=0; matrix=0;}
~dymatrix(){cout<<"Destructor called"<<endl;delete[] matrix;}
dymatrix(int inrows, int incolumns) //Parametrised objects, matrix database is defined here to store data.
{
rows = inrows;
columns = incolumns;
matrix = new double [inrows*incolumns];
for (int i=0; i<inrows*incolumns; i++)
{
matrix[i]=0;
}
}
int lengthr() const {return rows;} //Returns number of rows.
int lengthc() const {return columns;} //Return number of columns.
dymatrix &operator=( dymatrix &arr); //This is the assignment member function.
dymatrix(dymatrix&); //This is the deep copy member function.
dymatrix operator*(const dymatrix& arr)const ; //Overloading "*" operator.
double & operator[](const int n) //Overloading "[]" operator, this is important !!!
{
if(n<0 || n>=rows*columns)
{
cout<<"Error: trying to access matrix element out of bounds"<<endl;
exit(1);
}
return matrix[n];
}
int index(int j, int i) const //This member function returns the position of each index.
{
if (j > 0 && j <=rows && i > 0 && i <=columns)
{
//cout<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl;
return (i-1)+(j-1)*columns;
}
else {cout<<"Error, out of range"<<endl<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl; exit (1);}
}
double & operator()(int j, int i) const {return matrix[index(j,i)];} //The operator () returns the position of j and i in 1D array.
}; //Class End.
dymatrix::dymatrix(dymatrix &arr) //This is the copy constructor for deep copying.
{
matrix = 0; rows = arr.lengthr(); columns = arr.lengthc();
if (rows*columns >0)
{
matrix = new double [rows*columns];
for (int i =0; i < rows*columns; i++)
{
matrix[i] = arr[i];
}
}
}
dymatrix & dymatrix ::operator = (dymatrix &arr)
{
if(&arr == this) return *this; // no self assignment
delete[] matrix; matrix=0; rows=columns=0;
rows=arr.lengthr();
columns = arr.lengthc();
if(rows*columns>0)
{
matrix=new double[rows*columns];
// Copy values into new array
for(int i=0;i<rows*columns;i++) matrix[i] = arr[i];
}
return *this; // Special pointer!!
}
istream & operator >> (istream &is, dymatrix &om) //Overloading ">>" operator here to
{
cout<<"Please enter the number of rows you want"<<endl;
is >> om.rows; //Inputting number of rows.
cout<<"Enter the number of columns you want"<<endl;
is >> om.columns; //Inputting number of columns.
cout<<"Enter matrix"<<endl;
om.matrix = new double [om.rows*om.columns]; //Making a dynamic array here to put the data in.
for (int j = 1; j <= om.rows; j++)
{
for (int i = 1; i <= om.columns; i++)
{
is >> om.matrix[om.index(j,i)]; //Putting in the data into this dynamic array for each element.
}
}
return is;
}
ostream & operator << (ostream &os, const dymatrix &om) //To output the matrix in an standard matrix way
{
for(int j= 1; j<=om.rows; j++)
{
os<<endl<<endl;
for (int i = 1; i <=om.columns;i++)
{
os << om.matrix[om.index(j,i)]<<"\t"; //Similar method used in istream.
}
}
return os;
}
dymatrix dymatrix:: operator * (const dymatrix &arr) const //Overloading "*" operator.
{
if (columns != arr.rows)
{
cerr<<"SIZE DO NOT MATCH, YOU FAIL"<<endl; exit(1);
}
dymatrix new_matrix(rows,arr.columns);
for (int j = 1; j <= rows; j++)
{
for (int i = 1; i <= arr.columns; i++)
{
for (int k = 1; k <= columns; k++)
{
new_matrix.matrix[index(j,i)]= new_matrix.matrix[index(j,i)]+ matrix[index(j,k)]*arr(k,i);
cout<<"new_matrix = "<<new_matrix<<endl<<endl;
cout<<"k "<<k<<endl<<" arr.columns is "<<arr.columns<<endl<<"columns is "<<columns<<endl<<endl;
}
}
}
return new_matrix;
}
int main()
{
dymatrix a1;
cin >> a1; //Define the rows of the matrix
cout << a1<<endl<<endl;
dymatrix a2;
cin >> a2;
cout << a2<<endl<<endl;
dymatrix resu_a3;
resu_a3 = a1*a2;
cout<<"Multiplication = "<<resu_a3<<endl;
return 0;
}
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