在C ++中使用Eigen库时出错

Question

I am trying to use eigen library in c++, but getting error runtime.

#include<iostream>
#include <Eigen/Dense>
using namespace Eigen;
int main ()
{
    MatrixXd mat1;
    int i,j;
    i=4;
    j=3;
    mat1(i,j);
    float ct=1.0;


    for(int m=0;i<i;m++)
    {
        for (int n=0;n<j;n++)
        {
            mat1(m,n)= ct;
            ct = ct+1.0;
        }
    }

    std::cout<<"size of matrix is :"<<mat1.size()<<std::endl;
    std::cout<<"rows = "<<mat1.rows()<<"\t columns = "<<mat1.cols();
    //std::cout<<mat1;

}

I have Eigen library extracted at /usr/local/include/ and compiling as g++ test4.cpp -o test4 . There is no error at compile time. But at runtime, I get

test4: /usr/local/include/Eigen/src/Core/DenseCoeffsBase.h:365: Eigen::DenseCoeffsBase<Derived, 1>::Scalar& Eigen::DenseCoeffsBase<Derived, 1>::operator()(Eigen::Index, Eigen::Index) [with Derived = Eigen::Matrix<double, -1, -1>; Eigen::DenseCoeffsBase<Derived, 1>::Scalar = double; Eigen::Index = long int]: Assertion `row >= 0 && row < rows() && col >= 0 && col < cols()' failed.
Aborted (core dumped)

Any suggestions? Can someone also suggest how to use my typedef instead of predefined ones? Also, is there any special way to display matrix (as written in last line of code)?

Answer 1

mat1(i,j);

does not do what you think it does. It's the overloaded operator() and merely tries to access an element and returns a reference, it does not resize the matrix.

You need to either do

MatrixXd mat1(i,j);

or use

mat1.resize(i,j);