title: exponential function does not work in r but pol does
body: <p>I would like to fit/draw an exponential function but it does not work. For</p>
  
  <pre><code>before_database.frame&lt;- read.table("APD_data.txt", 
                                    header = TRUE,
                                    sep = "",
                                    dec="."
                                   )
  
  Single_APD.frame&lt;- before_database.frame[before_database.frame$Serial_number==912009913, ]
  
  # fit&lt;- lm(Voltage ~ poly(Amplification,2), data=Single_APD.frame)
  fit&lt;- lm(Voltage ~ exp(Amplification), data=Single_APD.frame)
  </code></pre>
  
  <p>I receive: </p>
  
  <pre><code>Error in lm.fit(x, y, offset = offset, singular.ok = singular.ok, ...) : 
    NA/NaN/Inf in 'x'
  </code></pre>
  
  <p>But " ~ poly(Amplification, 2)" works. What is wrong? I already searched for the error but the solutions do not work for me. 
  Thank you!</p>
  
  <p><a href="https://www.file-upload.net/download-12593733/APD_data.txt.html" rel="nofollow noreferrer">Data</a></p>