title: Difference between observations and variables in Matlab
body: <p>I'm kind of ashamed to even ask this but here goes. In every Matlab help file where the input matrix is a <code>NxD</code> matrix <code>X</code> Matlab describes the matrix arrangement as </p>
  
  <blockquote>
    <p>Data, specified as a numeric matrix. The rows of X correspond to
    observations, and the columns correspond to variables.</p>
  </blockquote>
  
  <p>Above taken from help of <a href="http://uk.mathworks.com/help/stats/kmeans.html#inputarg_X" rel="nofollow">kmeans</a> </p>
  
  <p>I'm kind of confused as to what does Matlab mean by observations and variables.</p>
  
  <p>Suppose I have a data matrix composed of 100 images. Each image is represented by a feature vector of size <code>128 x 1</code>. So here is 100 my observations and 128 the variables or is it the other way around?</p>
  
  <p>Will my data matrix be of the size <code>128 x 100</code> or <code>100 x 128</code></p>