title: How to abs a Expression in mosek.fusion.Model?
body: <p>I want to solve the optimization of maximizing the objective which is the sum of the absolute value of a matrix. However, I cannot find the accurate way to get that:</p>
  
  <p>for example:</p>
  
  <pre><code>import mosek.fusion as mf
  from mosek.fusion import Model, Domain, Expr, ObjectiveSense
  
  with Model('lol') as M:
      x = M.variable('x', [5,1], Domain.inRange(-1,1))
      M.objective('obj', ObjectiveSense.Maximize, abs(x))
      M.solve()
  </code></pre>
  
  <p>does not work </p>
  
  <pre><code>Type Error: bad operand type for abs(): 'RangedVariable'
  </code></pre>
  
  <p>How can I get the absolute value of <code>x</code>?</p>