Trevor Pythagoras

Ive been learning c++ and doing matrices in maths as well so I’ve decided to combine to the two in a simple command based program. The basic idea of the program is that it can quickly multiply matrices together and perform reflection and rotation transformations on them. Below is a download of the program and the source code. In the following weeks ill also make some tutorials on doing matrices by hand (click here for my multiplication lesson). Later im hoping to add some more features to it like finding the inverse matrix and the determinate

Download now !!!!!!!!!!

So how to use the program, well first of all type help. This will then display a list of the commands and what they do. When using it type your command, eg mlt, on its own, the program will then ask you to enter which is the first matrix and the second matrix in the multiplication. Every value should have the enter key pressed after its typed.

The program allows up to 10 matrices to be stored in memory plus the answer to the last calculation. They are stored in an array and are given numerical values. The first one you define, using dim, is matrix 0 the second is matrix 1 etc. The answer to the last calculation is matrix 10. When the program ask you which matrix you want to use it is asking you to enter this value for the matrix

Using the let command allows you to give one matrix the value of another. The first matrix number you enter is the one that the values being assigned to, the second is the value thats being assigned. This command is useful if you want to store the answer, after youve done the next calculation, to do this type let, when prompted type matrix that you want to be given the value of the answer and then give the value 10 for the value its being assigned.

Below is the code, i wrote it in visual c++ 2008, for the program. You may have to make changes if you using a diffrent complier to the includes at the top.

Enjoy using, but only to check, note all angles are in degrees recomplie if you want radians.

---

// matrix.cpp : main project file.

#include “stdafx.h”
#include <iostream>
#include <cmath>
#include <string>
using namespace std;

class mat
{
public:
double mata[20][3];
int lgth;
void dimmat()
{
cout << “enter length of matrix” << endl;
cin >> lgth;
//    cout << “” << endl;

for(int n=0;n<3;n++)
{
cout << “enter values for row” << n << ” , each followed by ‘enter’:” << endl;
for(int m=0;m<lgth;m++)
{
cin >> mata[n][m];
}
}
}

void display()
{
int rcount = 0;
int ccount = 0;

while(rcount < 3)
{
while(ccount < lgth)
{
//cout << “matrix:”<<endl;
cout << mata[rcount][ccount] << ” , “;

ccount++;
}
cout << ‘\n’;
ccount=0;
rcount++;
}
}

/*void rotate()
{
mat mat2;
mat2.dimmat();
mat mat3;
mat3 = mult(this, mat2);
}*/
};

mat mult(mat A, mat B)
{
cout << “multiply started” << endl;

//char pause;

mat ans;
ans.lgth=B.lgth;

int rcount = 0;
int ccount = 0;
int c2 = 0;

while(rcount < 3)
{
//cout << “row: ” << rcount << ” started” << endl;
while(ccount < A.lgth)
{
//cout << “collum: ” << ccount << “started” << endl;

ans.mata[rcount][ccount] = 0;
while(c2 < 3)
{
ans.mata[rcount][ccount] = ans.mata[rcount][ccount] + (A.mata[rcount][c2] * B.mata[c2][ccount]);
c2++;
}
//cout << “value is: ” << ans.mata[rcount][ccount] << endl;
//cin >> pause;
c2=0;
ccount++;
}
ccount=0;
rcount++;
}

int smelly;
ans.display();
return ans;
}

mat rotate(mat A, int angle)
{
mat T;
T.lgth = 3;

mat matans;

//creat transformation matrix
double pi = 3.14159265;
double theta = (angle*pi)/180;
T.mata[0][0] = cos(theta);
T.mata[0][1] = 0 – sin(theta);
T.mata[0][2] = 0;

T.mata[1][0] = sin(theta);
T.mata[1][1] = cos(theta);
T.mata[1][2] = 0;

T.mata[2][0] = 0;
T.mata[2][1] = 0;
T.mata[2][2] = 1;

matans = mult(T, A);
return matans;
}

mat reflect(mat A, int angle)
{
mat matans;
mat T;
T.lgth = 3;
//creat transformation matrix
double pi = 3.14159265;
double theta = (angle*pi)/180;
T.mata[0][0] = cos(2 * theta);
T.mata[0][1] = sin(2 * theta);
T.mata[0][2] = 0;

T.mata[1][0] = sin(2*theta);
T.mata[1][1] = 0 – cos(2*theta);
T.mata[1][2] = 0;

T.mata[2][0] = 0;
T.mata[2][1] = 0;
T.mata[2][2] = 1;

matans = mult(T, A);
return matans;
}

void input()
{
string dim = “dim”;

string com;
int end = 0;

mat matans;
int matcount = 0;
mat mats[11];
while(end == 0)
{
cout << “enter command>”;
getline(cin, com);

if(dim == com)
{
cout << “matrix” << matcount <<endl;
mats[matcount].dimmat();
matcount++;
}
if(com == “rot”)
{
cout << “which matirx?” <<endl;
int matnum;
cin >> matnum;
cout << “what angle (degrees)” << endl;
int rotang;
cin >> rotang;
matans = rotate(mats[matnum], rotang);
mats[10] = matans;
}
if(com == “rlt”)
{
cout << “which matirx?” <<endl;
int matnum;
cin >> matnum;
cout << “what angle (degrees)” << endl;
int rotang;
cin >> rotang;
matans = reflect(mats[matnum], rotang);
mats[10] = matans;
}
if(com == “ans”)
{
matans.display();
}
if(com == “mlt”)
{
cout << “first matrix” << endl;
int mat1;
cin >> mat1;
cout << “second matirx” << endl;
int mat2;
cin >> mat2;

matans = mult(mats[mat1], mats[mat2]);
mats[10] = matans;
}
if(com == “dsp”)
{
cout << “which matirx?” << endl;
int matdsp;
cin >> matdsp;
mats[matdsp].display();
}
if(com == “let”)
{
cout << “which matirx?” << endl;
int mat1;
cin >> mat1;
int mat2;
cout <<”eaqual to (10 is answer matrix)” << endl;
cin >> mat2;
mats[mat1] = mats[mat2];
}
if(com == “help”)
{
cout <<”Davids Woodfords matrix calculator” << endl;
cout << “takes the following commands” << endl;
cout <<” ‘dim’    ::  allows you to dfine a matrix”<< endl;
cout <<” ‘rot’    :: roates a matrix through an agnle” << endl;
cout <<” ‘rlt’    :: reflects a matrix through the line y=tan(a) where a is given” << endl;
cout <<” ‘ans’    :: displays the answer to the last calculation” << endl;
cout <<” ‘mlt’    :: lets u multiply 2 matricies together” << endl;
cout <<” ‘dsp’    :: displays a matrix specified”<<endl;
cout <<” ‘let’    :: allows u to assign one matrix the value of another, eg answer”<<endl;
cout<<”===================================================================”<<endl;
cout <<”matricies are sotred in an array of 10, with numerical values starting at 0″<<endl;
cout<<”matrix 10 is the answer matrix”<<endl;
cout<<”any parameters will be asked for wen needed”<<endl;

}
}

}

int main()
{
cout << “Welcome to David Woodfords Matrix calculator” << endl << endl;
cout<<”type ‘help’ for a list of commands” <<endl;
//    mat mata;
//    mata.dimmat();

/*    mat matb;
matb.dimmat();

mat matans;
matans = mult(mata, matb);
//    mata.display();
*/
//rotate(mata, 30);
input();
return 0;
}