# Unable to get Mahalanobis distance

I am trying to find the Mahalanobis distances between a test sample image and a few training data images (At&t database). I took http://answers.opencv.org/question/34... as reference for my code. When I run the code I am getting the following error

"OpenCV Error: Assertion failed (type == v2.type() && type == icovar.type() && sz == v2.size() && len == icovar.rows && len == icovar.cols) in Mahalanobis, file /home/opencv-2.4.9/modules/core/src/matmul.cpp, line 2244 "

Please find the code snippet for mahalanobis distance here http://pastebin.com/Mg8DbFQJ

```
Mat covar, invcovar, mean;
for(size_t sampleIdx = 0; sampleIdx < _projections.size(); sampleIdx++) {
calcCovarMatrix(_projections[sampleIdx], covar, mean, CV_COVAR_SCRAMBLED|CV_COVAR_ROWS,CV_64F); //Calculating the covariance matrix
invert(covar, invcovar, DECOMP_SVD); //Calculating the inverse covariance matrix
double dist=Mahalanobis( _projections[sampleIdx], q, invcovar );
// Add to the resulting distance array:
if(distances.needed()) {
distances.getMat().at<double>(sampleIdx) = dist;
}
if((dist < minDist) && (dist < _threshold)) {
minDist = dist;
minClass = _labels.at<int>((int)sampleIdx);
}
}
```