Function main

examples/matrix_ex.cpp:17–272

// ----------------------------------------------------------------------------------------

int main()
{
    // Let's begin this example by using the library to solve a simple 
    // linear system.
    // 
    // We will find the value of x such that y = M*x where
    //
    //      3.5
    // y =  1.2
    //      7.8
    //
    // and M is
    //
    //      54.2   7.4   12.1
    // M =  1      2     3
    //      5.9    0.05  1


    // First let's declare these 3 matrices.
    // This declares a matrix that contains doubles and has 3 rows and 1 column.
    // Moreover, its size is a compile time constant since we put it inside the <>.
    matrix<double,3,1> y;
    // Make a 3 by 3 matrix of doubles for the M matrix.  In this case, M is
    // sized at runtime and can therefore be resized later by calling M.set_size(). 
    matrix<double> M(3,3);
    
    // You may be wondering why someone would want to specify the size of a
    // matrix at compile time when you don't have to.  The reason is two fold.
    // First, there is often a substantial performance improvement, especially
    // for small matrices, because it enables a number of optimizations that
    // otherwise would be impossible.  Second, the dlib::matrix object checks
    // these compile time sizes to ensure that the matrices are being used
    // correctly.  For example, if you attempt to compile the expression y*y you
    // will get a compiler error since that is not a legal matrix operation (the
    // matrix dimensions don't make sense as a matrix multiplication).  So if
    // you know the size of a matrix at compile time then it is always a good
    // idea to let the compiler know about it.




    // Now we need to initialize the y and M matrices and we can do so like this:
    M = 54.2,  7.4,  12.1,
        1,     2,    3,
        5.9,   0.05, 1;

    y = 3.5,  
        1.2,    
        7.8;


    // The solution to y = M*x can be obtained by multiplying the inverse of M
    // with y.  As an aside, you should *NEVER* use the auto keyword to capture
    // the output from a matrix expression.  So don't do this: auto x = inv(M)*y; 
    // To understand why, read the matrix_expressions_ex.cpp example program.
    matrix<double> x = inv(M)*y;

    cout << "x: \n" << x << endl;