title: How to create Eigen matrix out of 2 vectors
body: <p>I have 2 vectors and a matrix:</p>
  
  <pre><code>VectorXd A;
  VectorXd B;
  MatrixXd C; 
  </code></pre>
  
  <p>How should I efficiently (without explicit loops and working fast)
  compute matrix C values so that</p>
  
  <pre><code>C(i,k) = A(i) * B(k);
  </code></pre>
  
  <p>Assume that matrix C already has appropriate dimensions. </p>
  
  <p>IMPORTANT: I only need help in using built-in Eigen syntax. Please no CUDA/MKL/BLAS suggestions. 
  Thank you.</p>