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 Author Comment/Response Nasser M. Abbasi 11/24/12 00:50am f1[x_] := Sin[2*Pi*x/10] + I*Cos[2*Pi*x/20] f2[x_] := Abs[f1[x]] f3[x_] := f2'[x] f3[1] -------------------------- Assuming the above is _supposed_ to work. Then the question is how can you be asking Mathematica to take derivative of a function with respect to a number? But to solve this, change f2'[x] to D[f2[x],x] And now you'll get the expected result that you can't do what you are trying to do: ---------------------- In[8]:= f3[1] During evaluation of In[8]:= General::ivar:1 is not a valid variable. >> Out[8]= D[Sqrt[5]/2, 1] ------------------------- --Nasser URL: ,

 Subject (listing for 'Derivative of a real function gives Complex res...') Author Date Posted Derivative of a real function gives Complex res... Dimanche 11/22/12 8:24pm Re: Derivative of a real function gives Complex... Nasser M. Ab... 11/24/12 00:50am Re: Derivative of a real function gives Complex... Sumit 11/24/12 02:03am Re: Re: Derivative of a real function gives Com... Dimanche 11/24/12 12:03pm
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