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 Author Comment/Response Sumit 11/24/12 02:03am Hi Dimanche, I think the problem is due to differentiability of Abs. You must have noticed "Abs'[]" in your output. So long you are interested in values Abs do its job perfectly. If you can define the derivative of Abs function the imaginary part will vanish. For example absolute[x_ + I y_] := Sqrt[x^2 + y^2] f1[x_] := Simplify[Sin[2*Pi*x/10] + I*Cos[2*Pi*x/20]] f2[x_] := absolute[f1[x]] f3[x_] := f2'[x] f3[1] // N 0.184658 Or if you want to stick with Abs then you have to teach him differentiation, like diff[f_, x_, x0_, h_] := 1/h (f[x0 + h/2] - f[x0 - h/2]) f1[x_] := Simplify[Sin[2*Pi*x/10] + I*Cos[2*Pi*x/20]] f2[x_] := Abs[f1[x]] x0 = 1; h = .0001; diff[f2, x, x0, h] 0.184658 Hope it will answer you. Best, -Sumit 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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