title: How to copy host vector to device vector by thrust
body: <p>I want to copy host <code>std::vector</code> to <code>thrust::device_vector</code> </p>
  
  <pre><code>std::vector&lt;double&gt; p_a(100)
  thrust::device_vector&lt;double&gt; d_vec
  </code></pre>
  
  <p>I want to copy <code>p_a</code> to <code>d_vec</code></p>