title: Is there a way to convert Expression into Variable in MOSEK
body: <p>I have a set of constraints in the following way, yet could not formulate it properly.</p>
  <p><a href="https://i.stack.imgur.com/L096g.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/L096g.png" alt="enter image description here" /></a></p>
  <p>In the following way, I could take the norm, but how can we get its power?</p>
  <pre><code>  Model::t M = new Model();
    auto start_ = new_array_ptr&lt;double, 1&gt;({-4, 0, 2});
    auto x_0 = M-&gt;variable(new_array_ptr&lt;int,1&gt;({3, 1}), Domain::unbounded());
    M-&gt;constraint(Expr::vstack(t-&gt;index(0), Expr::sub(x_0, start_)), Domain::inQCone());
  </code></pre>
  <p>If we can covert <code>Expr::sub(x_0, start_)</code> expression into a variable I could try to formulate norm followed by power, but still can't understand how to do this?</p>