title: R nls : could not find function "a"
body: <p>I'm trying to fit the information with nls() function.
  The formula is: <img src="https://i.stack.imgur.com/Yf2iw.gif" alt="enter image description here"></p>
  
  <p>but the R be angry :) </p>
  
  <pre><code>&gt; dk1
                          Q   H
                  1  43.754  21
                  2  74.434  52
                  3  94.601  72
                  4 115.327  81
                  5 135.751 109
                  6  72.990  54
                  7  35.756  12
                  8  36.685   2
                  9  35.799   2
  &gt; k1_H0
                  [1] 0
  &gt; n_N &lt;- nls(Q ~ a((H-k1_H0)^b)*(exp(1)^(c(log10(H-k1_H0)^2))), data = dk1, start = list( a = 0.1, b = 0.1, c=0.1), trace = T)
  Error in eval(expr, envir, enclos) : could not find function "a"
  </code></pre>