Problem in extracting SIFT feature vector..

I am trying to extract features using SIFT. I am using the fastsift library provided by source forge. The problem i am running into is, I am getting a 4XN frames and 128XN description for a single image. My doubt is how to reduce it to single row? The source code for SIFT http://sourceforge.net/projects/libsift/ After this I want to send the feature vector to svm?