title: Decision values in Libsvm
body: <p>I'm new to SVM. I used Libsvm for Matlab, and after a prediction phase I've got a decision values array. From SVM theory: each test record z is assigned as positive if </p>
  
  <blockquote>
    <p>f(z)=1</p>
  </blockquote>
  
  <p>where f(z) is defined as </p>
  
  <blockquote>
    <p>f(z)=sign(w*z+b)</p>
  </blockquote>
  
  <p>So how can I relate the decision value from the array for an instance z with f(z)?
  Is the prediction based on decision value so: if dec_value>0 then z is positive otherwise z is negative?</p>