OpenCV solve equation

Hello,

I'm hoping that there is somebody out there who is familiar with OpenCV, as I have a very simple problem.

I have a linear equation Ax = B which I want to solve. This is done with the OpenCV function solve(A, B, x). (A fourth argument can be used to specify the method for solving.) However, I am not getting the correct results.

For example, consider this code for a very simple equation:

Code:

---

Mat A(2, 2, CV_32F);
Mat B(2, 1, CV_32F);
Mat x(2, 1, CV_32F);

A.data[0] = 2;
A.data[1] = 1;
A.data[2] = 1;
A.data[3] = 1;
B.data[0] = 4;
B.data[1] = 3;

solve(A, B, x);

cout << "x0 = " << (float)x.data[0] << ", x1 = " << (float)x.data[1] << endl;

---

This is solving the following equation:

{ 2 1 } { x0} = { 4 }
{ 1 1 } { x1} = { 3 }

And I get the solution: x0 = 182, x1 = 62.

This is clearly wrong. The correct solution should be: x0 = 1, x1 = 2.

I have tried all the different solver types as the fourth argument, and they all return the same result.

What am I doing wrong?

Thanks!

If you have the source code, why not debug into the solve() function to see what it's doing?

Regards,

Paul McKenzie

You are instructing the matrix to create itself as if it contains floats (CV_32F), but when you access the data pointer directly, its type is unsigned char*. Therefore, your assignments are not doing what you think they are doing.

You have two options. Either you can use the setTo() or at<float>() method instead, which will do the type conversion, or you can use the Mat_<float> template rather than the Mat class, so that it knows its type at compile time and its operator() will do the write thing.