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Student Support Forum: 'Problem with Abs and D' topicStudent Support Forum > General > "Problem with Abs and D"

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Daniele Lupo
10/04/05 5:57pm

Hi to all.

I've a problem with the derivative of Abs.

Considering, for example, this function

a = Abs[Sqrt[s + x]]

If (with mathematica 5.1), I use this command

D[a, x]

I obtain this

Derivative[1][Abs][s + x]/(2*Sqrt[Abs[s + x]])

It containts Abs'[..] that's not right.

If I use PiecewiseExpand in this way

PiecewiseExpand[a]

I don't obtain nothing, while in this way

PiecewiseExpand[a, Reals]

I obtain

Piecewise[{{Sqrt[-s - x], s + x < 0}}, Sqrt[s + x]]

But In this case I consider all variables as real. Instead I want that x is real, while s is complex, and making an expansion with these assumptions. How can I do it?

Thanks for answers

Daniele




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Subject (listing for 'Problem with Abs and D')
Author Date Posted
Problem with Abs and D Daniele Lupo 10/04/05 5:57pm
Re: Problem with Abs and D Forum Modera... 11/23/05 1:48pm
Re: Problem with Abs and D Peter Pein 11/23/05 8:57pm
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