> nlsLM(formula, data=data, start=init_cond)
Nonlinear regression model
  model: y ~ d + (a - d)/(1 + (x/c)^b)
   data: data
      a       b       c       d 
-0.2066  0.5437 60.3938  2.8999 
 residual sum-of-squares: 0.006767

Number of iterations to convergence: 16 
Achieved convergence tolerance: 1.49e-08