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Re: Modulus / Absolute Value

  • To: mathgroup at
  • Subject: [mg90080] Re: [mg90058] Modulus / Absolute Value
  • From: Murray Eisenberg <murray at>
  • Date: Sat, 28 Jun 2008 05:52:15 -0400 (EDT)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <>
  • Reply-to: murray at

What problem are you actually trying to solve?  (You do not say!)

Why are you using awkward LaTeX mark-up here?  (Since you have a 
Mathematica question, why not start with Mathematica notation?  Type it 
into a Mathematica notebook, then use Edit > Copy As > Plain Text to 
copy it into your e-mail message.)

What does the function g have to do with this?  (I don't see its 
relevance at all; I think your question is really about integrating f, 
isn't it?)

Possibly the question you are asking is, in effect, how to find the 
total area enclosed between the graph of

   f[x_] := Sin[2x]

and the x-axis over the interval from 0 to Pi.  This is simply:

   Integrate[ Abs[f[x]], {x, 0, Pi} ]

Perhaps you wanted to add to that the area enclosed by the graph of g 
and the x-axis, over that same interval.  You could add to the preceding 
the value of

   Integrate[ Abs[g[x]], {x, 0, Pi} ]

or, since g[x]<= 0 when 0 <=x <= Pi, simply add

   - Integrate[g[x], {x, 0, Pi} ]

Felipe Mannshardt wrote:
> Greetings,
> i have been searching the way to tell Mathematica to use Modulus / Absolute Value.  I have been unable to find.
> \left(\int_0^{\frac{\pi }{2}} f[x] \, dx+\int_{\frac{\pi }{2}}^{\pi } f[x] \, dx\right)+\int_0^{\pi } g[x] \, dx
> I should be subtracting the upper Integral from the lower Integral,
> but since i could not find a way to tell Mathematica to use Modulus /Absolute Value.  I had to add the upper to the lower . . .
> my functions are, f and g
> f[\text{x$\_$}]\text{:=}\text{Sin}[2*x]g[\text{x$\_$}]\text{:=}x^2-(\pi *x)
> So, can some1 help me out with this one? How to use Modulus/Absolute Value (German, Betrag) with Mathematica.

Murray Eisenberg                     murray at
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305

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