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constraints and NMinimize


Hi,

Let's suppose I want to minimize this function numerically
f[x_, om_] := 1/Sqrt[-(om^2 - 1)(x - 1)^2/4 + x]

I do

NMinimize[{f[x, om],
om > 0 && x > (-1 + om)/(1 + om) && x < (1 + om)/(-1 + om)}, {x, om}]

so I have included constraints so that the argument of the square root 
in the definition of the function is always positive.

However I get this error:

NMinimize::nrnum: The function value 15268.5-
342.001\[ImaginaryI] is not a real number at {ol, om} = {1.69091, 
0.137466}.

Is there any elegant way to avoid getting this message? (Apart from 
swithching off that kind of messages, of course).

Thanks a lot,

Ruth


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