Dear all,

I have a problem using the R finction nls. I am trying to perform an 
optimisation of the volatility parameter in the Black and Scholes formula. In 
the function nls I wrote as a formula the  call option price with the only 
unknown parameter the volatility that I called theta.  The code is the 
following and I have recevied some errors, one is that below. In my code I use 
as data a dataset of simuleted option price of length 99, and the same I did 
for subset.  I would like to have a code that compare my model with the 
volatility as an unknown parameter with a set of gien option data. Thanks in 
advance.



optim<- nls(call ~ 
S*pnorm((log(15/14)+(0.015+theta^2/2)*0.17)/(theta*sqrt(0.17))) - 
14*exp(-0.015*0-17)*pnorm((log(15/14)+(0.015+theta^2/2)*0.17)/(theta*sqrt(0.17))
 - theta * sqrt(0.17)), data=data, start= 0.01, control= nls.control(maxiter = 
50, tol = 1e-05, minFactor = 1/1024,                        printEval = FALSE, 
warnOnly = FALSE),  subset= "data1")


Error in nls(call ~ S * pnorm((log(15/14) + (0.015 + theta^2/2) * 0.17)/(theta 
*  :
  parameters without starting value in 'data': theta


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