st: could not calculate numerical derivatives

[vesile kutlu <kutlu.vesile@gmail.com>]

Hi all,
I am trying to solve the function “v” numerically in Mata but I get
the error ” could not calculate numerical derivatives -- discontinuous
region with missing values encountered”.  I ask Mata to minimize this
function with respect to a and b. I provide the initial values of
these parameters. Is there something wrong with my code? I would
appreciate if you could tell me why I got this error? Is there maybe
another way to solve this problem? Thank you.
Vesile
void mysolver(todo, p, v, S, H)
  {
  a=p[1]
  b=p[2]
  v=(0.7-exp((a/b)*(exp(b*48)-exp(b*75))))^2+(0.4-exp((a/b)*(exp(b*48)-exp(b*80))))^2
  }
  S=optimize_init()
  optimize_init_evaluator(S, &mysolver())
  optimize_init_evaluatortype(S, "v0")
  optimize_init_params(S, (1,1))
  optimize_init_which(S, "min")
  p=optimize(S)
  p
  end

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