eigen-2.1.1: eigen3/doc/examples/Tutorial_ReductionsVisitorsBroadcasting_rowwise.cpp

#include <iostream>
#include <Eigen/Dense>

using namespace std;
int main()
{
  Eigen::MatrixXf mat(2,4);
  mat << 1, 2, 6, 9,
         3, 1, 7, 2;
  
  std::cout << "Row's maximum: " << std::endl
   << mat.rowwise().maxCoeff() << std::endl;
}