title: Sum notation in julia?
body: <p>I was wondering if anyone knew of a julia equivalent function to a sum using sigma.
  For example if I wanted a sum of this sort (unsure of how to show sigma notation, so here is a picture of what I am looking for):</p>
  
  <p><a href="https://i.stack.imgur.com/PXBdi.png" rel="noreferrer"><img src="https://i.stack.imgur.com/PXBdi.png" alt=""></a></p>
  
  <p>Both <code>c</code> and <code>x</code> would be matrices that I would define earlier in the code. Does anyone know how to code this in Julia or whether julia has an equivalent function?<br>
  I have used <code>sum</code> for more simple vector sums, but I am not sure if that would translate to much larger matrices. Any ideas?</p>