title: downwards arrow in R-plot axis label
body: <p>I have a Variable named <strong>\LW$_\downarrow$</strong> in Latex. 
  As you can imagine, i would like to use the same phrase as axis label and add the Unit which is [W/m²] or [W m^-2] </p>
  
  <p>I managed to do this:</p>
  
  <pre><code>library(ggplot2)
  data &lt;- data.frame(x=c(1:5), y=c(2:6))
  ggplot(data = data, aes(x=x, y=y))+
    geom_point()+
    labs(x=expression(LW%down%. ))
  </code></pre>
  
  <p>but </p>
  
  <pre><code>ggplot(data = data, aes(x=x, y=y))+
    geom_point()+
    labs(x=expression(LW%down% )) #no point behind the second %
  </code></pre>
  
  <p>gives "Error: </p>
  
  <blockquote>
    <p>unexpected ')' in: "  geom_point()+   labs(x=expression(LW%down% )"</p>
  </blockquote>
  
  <p>and </p>
  
  <pre><code>ggplot(data = data, aes(x=x, y=y))+
    geom_point()+
    labs(x=paste(expression(LW%down%. ), "[W/m²]"))
  </code></pre>
  
  <p>gives this: with %down% as word</p>
  
  <p><a href="https://i.stack.imgur.com/HIXpv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HIXpv.png" alt="enter image description here"></a></p>
  
  <p>unfortunately not very helpful.</p>
  
  <p>I hope someone can help. I have a lot of plots so I hope someone so manual editing with inkscape does not really sound like a good option.</p>
  
  <hr>
  
  <p>tyumru gave me a good hint to the right direction with</p>
  
  <pre><code>ggplot(data = data, aes(x=x, y=y))+
    geom_point()+
    labs(x=expression("LW"%down%"[W/m²]"))
  </code></pre>
  
  <p>Whe I try to put the arrow in subscript with </p>
  
  <pre><code>ggplot(data = data, aes(x=x, y=y))+
    geom_point()+
    labs(x=expression("LW"[%down%]"[W/m²]"))
  </code></pre>
  
  <p>Unfortunately I get</p>
  
  <p>Error: unexpected SPECIAL in:
  "  geom_point()+
    labs(x=expression("LW"[%down%"</p>