title: How do I use System.Numerics in Mono C# in MonoDevelop?
body: <p>When I have this line at the top of my file:</p>
  
  <pre><code>using System.Numerics;
  </code></pre>
  
  <p>I get the following error:</p>
  
  <p><code>Error CS0234: The type or namespace name 'Numerics' does not exist in the namespace 'System' (are you missing an assembly reference?) (CS0234) (CSharpTests)
  </code></p>
  
  <p>Other <code>using</code> directives at the top of my file, such as <code>using System;</code>, work just fine.</p>
  
  <p>I'm using Mono 5.12.0.301 and MonoDevelop 7.5 (build 1255) on Ubuntu 18.04 64-bit.</p>
  
  <p>One of my first thoughts was that the framework version was set to something old enough to not have <code>System.Numerics</code>. In Options -> Build -> General, my framework version is the default of 4.5, and changing it to the latest version of 4.7.1 does not make the code work:</p>
  
  <p><a href="https://i.stack.imgur.com/AWfPW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AWfPW.png" alt="Framework Version Build General"></a></p>
  
  <p><a href="https://stackoverflow.com/a/16631284/4441547">This answer</a> found that the problem was with an outdated framework version, but clearly I have a new enough framework version, right?</p>
  
  <p>EDIT: Ok, with SushiHangover's answer I'm able to use System.Numerics, but I'm actually trying to use System.Numerics.Vectors, which I have included in References:</p>
  
  <p><a href="https://i.stack.imgur.com/5zJ24.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5zJ24.png" alt="System Numerics Vectors"></a></p>
  
  <p>But when I use <code>using System.Numerics.Vectors;</code> I get this error:</p>
  
  <p><code>Error CS0234: The type or namespace name 'Vectors' does not exist in the namespace 'System.Numerics' (are you missing an assembly reference?) (CS0234) (CSharpTests)
  </code></p>