Unexpected Harris Detector results - c++

Question

I load the vertical and horizontal gradients into the function posted here and it calculates the sums which than make up the corner response. Why do only boarder pixels get to be found, my threshold is 0 otherwise there is 0 corners on the image. For gradients I used sobel operator.
Look at the output image below.
for (int i = 0; i < width; i++)
{
for (int j = 0; j < height; j++)
{
if ((i - search_size / 2 < 0 || i + search_size / 2 > image1.rows - 1) || (j - search_size / 2 < 0 || j + search_size / 2 > image1.cols - 1)) {
continue;
}
double Ix2 = 0, Iy2 = 0, Ixy = 0;
double detM=0;
double traceM=0;
double R = 0;
for (int m = i-search_size /2; m < i + search_size /2 ; m++){
for (int n = j-search_size /2; n < j + search_size/2 ; n++){
gauss = exp(-(((i - m) * (i - m)) + ((j - n) * (j - n))) / gaus_del);
//Compute Ix^2 , Iy^2 and Ixy
Ix2 += gauss*(image1.at<float>(m, n)*image1.at<float>(m, n));
Iy2 += gauss*(image2.at<float>(m, n)*image2.at<float>(m, n));
Ixy += gauss*(image1.at<float>(m, n)*image2.at<float>(m, n));
}
}
detM = (Ix2*Iy2 - Ixy*Ixy);
traceM = Ix2*Ix2 + Iy2*Iy2;
R = detM / traceM;
//cout <<i+j<< endl;
// std::cout << "R :" << Iy2 << endl;
if (R > threshold)
{
circle(image, cv::Point2f(i, j), 3.5, cv::Scalar(255, 255, 0), 1, 5);
cout << "corner found" << endl;
}
}
}
EDIT : i am using uchars now and the result looks alot better
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