(C++) boost::numeric::ublas::matrix example 3: inverse of a 2x2 matrix

 

boost::numeric::ublas::matrix example 3: inverse of a 2x2 matrix is a Boost.uBLAS library example.

 

• Download the Qt Creator project 'CppUblasMatrixExample3' (zip)

 

 

 

 

 

Technical facts

 

Application type(s)

• Desktop application

Operating system(s) or programming environment(s)

• Lubuntu 12.10 (quantal)

IDE(s):

• Qt Creator 2.5.2

Project type:

• Console application

C++ standard:

• C++98

Compiler(s):

• G++ 4.7.2

Libraries used:

• STL: GNU ISO C++ Library, version 4.7.2

 

 

 

 

 

Qt project file: CppUblasMatrixExample3.pro

 

---

TEMPLATE = app CONFIG += console CONFIG -= qt SOURCES += main.cpp

 

 

 

 

 

main.cpp

 

---

#include <boost/numeric/ublas/matrix.hpp> const boost::numeric::ublas::matrix<double> Inverse(   const boost::numeric::ublas::matrix<double>& m) {   assert(m.size1() == m.size2() && "Can only calculate the inverse of square matrices");   assert(m.size1() == 2 && m.size2() == 2 && "Only for 2x2 matrices");   boost::numeric::ublas::matrix<double> n(2,2);   const double a = m(0,0);   const double b = m(0,1);   const double c = m(1,0);   const double d = m(1,1);   assert((a * d) - (b * c) != 0.0 && "Determinant must be nonzero");   const double determinant = 1.0 / ((a * d) - (b * c));   n(0,0) =  d * determinant;   n(0,1) = -b * determinant;   n(1,0) = -c * determinant;   n(1,1) =  a * determinant;   return n; } const boost::numeric::ublas::matrix<double> CreateMatrix() {   boost::numeric::ublas::matrix<double> m(2,2); //y-x-ordered   m(0,0) = 4.0;   m(0,1) = 7.0;   m(1,0) = 2.0;   m(1,1) = 6.0;   return m; } bool IsAboutEqual(const double x, const double y) { return std::abs(x-y) < 0.00001; } int main() {   //Create an example matrix   const boost::numeric::ublas::matrix<double> m = CreateMatrix();   assert(IsAboutEqual(m(0,0),4.0)); assert(IsAboutEqual(m(0,1),7.0));   assert(IsAboutEqual(m(1,0),2.0)); assert(IsAboutEqual(m(1,1),6.0));   //Obtain the inverse of the example matrix   const boost::numeric::ublas::matrix<double> n = Inverse(m);   assert(IsAboutEqual(n(0,0), 0.6)); assert(IsAboutEqual(n(0,1),-0.7));   assert(IsAboutEqual(n(1,0),-0.2)); assert(IsAboutEqual(n(1,1), 0.4));   //Check that the product of a matrix and its inverse yields an identity matrix   const boost::numeric::ublas::matrix<double> p = boost::numeric::ublas::prod(m,n);   assert(IsAboutEqual(p(0,0),1.0)); assert(IsAboutEqual(p(0,1),0.0));   assert(IsAboutEqual(p(1,0),0.0)); assert(IsAboutEqual(p(1,1),1.0)); }