Re: [eigen] Not able to solve the system of equation having vector as coefficient of the matrix

[Adrien Escande <adrien.escande@xxxxxxxxx>]

Dear Rohit,

is there any particular reasons that you explicitely want the elements in your matrices to be 2d vectors? From a mathematical point of view, your problem seems ill-formed: 2d-vectors are not invertible.

If you just need to form matrices from 2d-vector, replace every Eigen::Matrix<Eigen::RowVector2d, 2, 2> with  Eigen::Matrix<double, 4, 2> in your code, and you're set.

Note that A being 4-by-2, your system is under-determined, and your solution will be a 2-by-2 matrix. Is it really what you are looking for, or do you want to solve two separate systems, one with the first elements of all your vectors, and the other with the second elements?

Best regards,

Adrien

On Wed, Jun 5, 2019 at 4:07 AM Rohit Aggarwal <cs18mtech11030@xxxxxxxxxx> wrote:

Hi All,

We are trying to use eigen solver api to solve the problem in which we have a matrix containing vector as the coefficient of it.
Form Ax=B
Able to create a matrix for A(2,2) having a vector like
[ [1,2],[3,4]
  [5,6],[7,8] ]

Matrix B(2,1)
[ [1,2]
  [1,1] ]

But when I am trying to pass the value to the solver, it is giving fatal error (Eigen/src/SVD/JacobiSVD.h:714:15: error: no matching function for call to ‘abs(const Scalar&)’          if(abs(m_workMatrix.coeff(p,q))>threshold || abs(m_workMatrix.coeff(q,p)) > threshold).)

Please look into it and suggest what I m missing.

#include <iostream>
#include "Eigen/Dense"
using namespace std;
using namespace Eigen;
int main()
{
Eigen::Matrix< Eigen::RowVector2d, 2, 2> A;
Eigen::Matrix< Eigen::RowVector2d, 2, 1> B;

RowVector2d rv1;
RowVector2d rv2;
RowVector2d rv3;
RowVector2d rv4;

rv1 << 1,2;
rv2 << 3,4;
rv3 << 5,6;
rv4 << 7,8;
cout << "Here is the matrix rv1:\n" << rv1 << endl;
cout << "Here is the matrix rv2:\n" << rv2 << endl;
cout << "Here is the matrix rv3:\n" << rv3 << endl;
cout << "Here is the matrix rv4:\n" << rv4 << endl;


A << rv1,rv2, rv3, rv4;

RowVector2d b1;
RowVector2d b2;
b1 << 1,2;
b2 << 2,1;

B << b1, b2;
cout << "Here is the matrix B(0,0):\n" << B(0,0) << endl;
cout << "Here is the matrix B(0,1):\n" << B(1,0) << endl;

JacobiSVD<Eigen::Matrix<Eigen::RowVector2d, 2, 2>> dec(A);

}

-Rohit Aggarwal