title: Is a Google Sheets fit model a valid place to retrieve starting parameters for nls()?
body: <p>I am trying to fit an exponential model of form <code>y = a*e^(x*b)</code> in R to the data I have ran below, using the <code>nls()</code> function. I have read here and in other places that I need to feed the model reasonable parameters for <code>a</code> and <code>b</code>, but the way about getting those starting parameters seems very variable, and many of the suggested ways were methods that I could not find elaborations on. One suggestion said that you could copy your data into an Excel spreasheet, fit your model on the graph, and adjust the parameters until it appeared to fit the data reasonably well. Well, I went into Google Sheets, I inserted a chart based on the data below, and then selected <code>Customize &gt; Series &gt; Trendline (exponential)</code>, and it fed me a formula of <strong>5.51e^0.015x</strong> . Are these valid values I could use as my starting parameters? Does Google Sheets produce those effectively, or do I need to do the tinkering method, or try something else? I have read over and over again the importance of choosing proper starting values, so any help on this would be much appreciated. My educational background did not cover non linear models.</p>
  <pre><code>x       y
  19.005  5.49
  18.19   6
  19.59   5.885
  19.93   8.96
  17.615  13.85
  18.795  2.72
  19.11   8.09
  19.885  8.11
  15.76   6.66
  16.48   6.27
  15.805  5.375
  15.825  3.06
  15.985  7.795
  15.755  6.255
  15.485  5.925
  15.475  9.925
  16.45   6.055
  16.285  5.24
  15.92   11.15
  16.775  5.57
  16.075  3.275
  16.475  5.635
  16.825  4.72
  16.28   2.035
  17.26   6.07
  17.245  4.9
  17.98   8.06
  17.35   6.94
  18.22   7.8
  16.27   12.2
  17.555  7.335
  16.98   5.76
  17.415  7.51
  17.5    6.18
  </code></pre>