title: Error:attempt to apply non-function
body: <p>I'm trying to run the following code in R, but I'm getting an error.</p>
  
  <p>I'm not sure what part of the formula is incorrect. Any help would be greatly appreciated.</p>
  
  <pre><code>&gt; censusdata_20$AGB93 = WD * exp(-1.239 + 1.980 * log (DIAM93) + 0.207 (log(DIAM93))^2 
                          - 0.0281 (log(DIAM93))^3)
  Error: attempt to apply non-function
  </code></pre>