eigen/unsupported/doc/examples/MatrixFunction.cpp

#include <unsupported/Eigen/MatrixFunctions>
#include <iostream>

using namespace Eigen;

std::complex<double> expfn(std::complex<double> x, int)
{
  return std::exp(x);
}

int main()
{
  const double pi = std::acos(-1.0);

  MatrixXd A(3,3);
  A << 0,    -pi/4, 0,
       pi/4, 0,     0,
       0,    0,     0;

  std::cout << "The matrix A is:\n" << A << "\n\n";
  std::cout << "The matrix exponential of A is:\n" 
            << A.matrixFunction(expfn) << "\n\n";
}