Matrix-Toolbox (under active construction)

A simple C++ library to help you with matrix computations.

Documentation

To use the library, please #include "mymatrix.h".

Define a matrix.

Initialize with the number of rows and columns.

int row = 10;
int col = 5;
Matrix mat(row, col);

Initialize with a row vector of doubles.

vector<double> rowV; 
// ... add elements into rowV
Matrix mat(rowV);

Initialize from another matrix.

Matrix matA(mat);

Basic Operations

1. get the size of the matrix

mat.size(0) returns the number of rows.

mat.size(1) returns the number of columns.

2. access an element

Notice: Matrix index starts from ZERO.

double x = mat.get(0, 1); mat.set(0, 1, x);

3. convert into vector of vectors

vector<vector<double> > V = mat.toVector();

4. Row/Column Operations

Access the i-th row. (0 <= i < #rows)

Matrix r = mat.getRow(i);

Access the j-th column. (0 <= j < #col)

Matrix c = mat.getColumn(j);

Modify the i-th row.

Matrix new_row(mat.size(0), 1);
// add elements into new_row
mat.setRow(i, new_mat);

Modify the j-th column.

Matrix new_col(1, mat.size(1));
// add elements into new_row
mat.setCol(j, new_mat);

Add new rows under the last row.

The appendRow member function takes a vector<double> or a Matrix with the same number of columns as parameter.

mat.appendRow(rowV); 
mat.appendRow(new_mat);

Add new columns after the last column.

mat.appendCol(rowV); 
mat.appendCol(new_mat);

new_mat must have the same number of rows.

Swap two rows.

// swap the first and second row
mat.swap(0, 1); 

5. Splitting

Horizontal split over a matrix indicated by its column index.

vector<int> vec;
vec.push_back(0);
vec.push_back(2);
vector<Matrix> split_mats = mat.hsplit(vec);
//split_mats[0] is the first column of mat
//split_mats[1] is the third column of mat

Split all columns. Pass no parameters.

vector<Matrix> split_mats = mat.hsplit();

The same to vertical splitting, with vspilt and row index as parameters.

To split all rows, pass no parameters.

6. Simple computation

overloaded operators

Matrix & Matrix

Matrix matA;
Matrix matB;
// ... initialization
Matrix result;
result = matA + matB; // addition
result = matA - matB; // subtraction
result = matA * matB; // matrix multiply. matA column number == matB row number

bool equal = (matA == matB);
bool noneq = (matA != matB);

Matrix & scalar

result = matA * 0.01; // element-wise multiply
result = 0.01 * matA;
result = matA / 2;	// element-wise division

Notice: 0 means row operations. 1 means column operations.

Sum up elements along rows.

Matrix sum = mat.sum(0);

Sum up elements along columns.

Matrix sum = mat.sum(1);

The same to product, max, and min.

Elements multiplication, maximum or minimum element along rows/columns, respectively.

Sum up all matrix elements.

double sum = mat.sum();

Multipliy all matrix elements.

double product = mat.product();

Get the mean of each row or column with mat.mean(i).

Get the variance of each row or column with mat.variance(i).

Sort rows or columns with mat.sort(i).

7. Linear algebra

Inverse of a square matrix using Gauss-Jordon method.

Matrix inv = mat.inverse();
// or 
#include "matlab.h"
Matrix inv = matlab::inverse(mat);