title: Numpy Matrix Subtraction Confusion
body: <p>I have a question about the result of an operation I accidentally performed with two numpy matrices (and later fixed). </p>
  
  <p>Let's say that I have a column vector, A = [1,2,3], and a row vector B = [1,1,1]. As far as I know there is no correct mathematical way to "subtract" these two vectors, i.e. this should be an undefined operation. And yet, when I do so, I get back:</p>
  
  <pre><code>&gt;&gt;&gt; matrix([[0, 1, 2],
              [0, 1, 2],
              [0, 1, 2]])
  </code></pre>
  
  <p>I thought that this might be some sort of broadcasting operation, but this still troubles me a bit. Shouldn't numpy.matrix objects only contain mathematically valid matrix operations? </p>
  
  <p>Any help is appreciated!</p>
  
  <p>Thanks!</p>