title: Kohonen SOM Maps: Normalizing the input with unknown range
body: <p>According to "Introduction to Neural Networks with Java By Jeff Heaton", the input to the Kohonen neural network must be the values between -1 and 1.</p>
  
  <p>It is possible to normalize inputs where the range is known beforehand:
  For instance RGB (125, 125, 125) where the range is know as values between 0 and 255:
  <br/>
  1. Divide by 255: (125/255) = 0.5 >> (0.5,0.5,0.5) <br/>
  2. Multiply by two and subtract one: ((0.5*2)-1)=0 >> (0,0,0)<br/></p>
  
  <p>The question is how can we normalize the input where the range is unknown like our height or weight. </p>
  
  <p>Also, some other papers mention that the input must be normalized to the values between 0 and 1. Which is the proper way, "-1 and 1" or "0 and 1"?</p>