title: Distance between hyperplanes
body: <p>I'm trying to teach myself some machine learning, and have been using the MNIST database (<a href="http://yann.lecun.com/exdb/mnist/" rel="noreferrer">http://yann.lecun.com/exdb/mnist/</a>) do so. The author of that site wrote a paper in '98 on all different kinds of handwriting recognition techniques, available at <a href="http://yann.lecun.com/exdb/publis/pdf/lecun-98.pdf" rel="noreferrer">http://yann.lecun.com/exdb/publis/pdf/lecun-98.pdf</a>.</p>
  
  <p>The 10th method mentioned is a "Tangent Distance Classifier". The idea being that if you place each image in a (NxM)-dimensional vector space, you can compute the distance between two images as the distance between the hyperplanes formed by each where the hyperplane is given by taking the point, and rotating the image, rescaling the image, translating the image, etc.</p>
  
  <p>I can't figure out enough to fill in the missing details. I understand that most of these are indeed linear operators, so how does one use that fact to then create the hyperplane? And once we have a hyperplane, how do we take its distance with other hyperplanes?</p>