CODEWITHSUNDEEP
c++eigenvalueopencv3.2
Anirudh
Anirudh

Reputation: 558

error in computing eigen values

I am trying to find eigen values for a syymetric matrix as follows:-

    Mat t(2, 2, CV_32F); 
    t.at<float>(0, 0) = 1;
    t.at<float>(0, 1) = 0;
    t.at<float>(1, 0) = 0;
    t.at<float>(1, 1) = 128;

    Mat eigVal,eigVec;
    eigen(t,eigVal,eigVec);

When I am printing the eigen values for this matrix it gives me correct answer.

cout << eigVal.at<float>(0) << "," << eigVal.at<float>(1) << "\n";

The output which I get is 128,1. But when I am changing my matrix as follows:-

t.at<float>(0, 0) = 4;
t.at<float>(0, 1) = 2;
t.at<float>(1, 0) = 1;
t.at<float>(1, 1) = 3;

I am not getting correct response. The output which I am expecting is 5,2. But instead I am getting output as 5.56155 and 1.43845. Can anyone tell me where I did mistake

Upvotes: 0

Views: 107

Answers (1)

Heath Raftery
Heath Raftery

Reputation: 4209

eigen only works on symmetric matrices (those with equal values of either side of the main diagonal). You need eigenNonSymmetric for non-symmetric matrices:

#include <stdio.h>
#include <opencv2/opencv.hpp>

using namespace cv;
using namespace std;

int main(int argc, char *argv[])
{
  Mat t(2, 2, CV_32F);
  t.at<float>(0, 0) = 4;
  t.at<float>(0, 1) = 2;
  t.at<float>(1, 0) = 1;
  t.at<float>(1, 1) = 3;

  Mat eigVal,eigVec;
  eigenNonSymmetric(t,eigVal,eigVec);

  cout << eigVal.at<float>(0) << "," << eigVal.at<float>(1) << "\n";

  return 0;
}

Output:

5,2

Upvotes: 1

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