       Re: New Analytical Functions - Mathematica Verified

• To: mathgroup at smc.vnet.net
• Subject: [mg66853] Re: New Analytical Functions - Mathematica Verified
• From: "Mohamed Al-Dabbagh" <mohamed_al_dabbagh at hotmail.com>
• Date: Thu, 1 Jun 2006 06:55:41 -0400 (EDT)
• References: <200605280104.VAA23436@smc.vnet.net><e5jss1\$e73\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Daniel Lichtblau wrote:
> Mohamed Al-Dabbagh wrote:
> > Abstract: An attempt was made to analytically describe some basic
> > functions which are provided with the libraries of mathematical
> > functions of programming languages. This study will rely on Mathematica
> > in calculating all numerical results. This study provides global
> > methods to calculate some discrete functions, which were previously
> > calculated by using low-level language techniques to chop digits. Using
> > these definitions we can simulate digital signals without the need for
> > IF statements and conditions.
> >
> > A comparison were made between the formulas provided by this study and
> > some functions provided by Mathematica such as FractionalPart function
> > that converges very slowly or does NOT converge at all to correct
> > results. The formulas derived herein were applied to complex numbers
> > and some interesting results were obtained, such as the integer part of
> > a complex number equals the Floor of its real part, and will be without
> > imaginary part, i.e. the integer part of a complex number is a real
> > number!
> >
> > http://dabbagh2.fortunecity.com/disc/
> >
> > Mohamed Al-Dabbagh
>
> I'll point out some things with regard to your reformulation of a
> sawtooth in terms of elementary functions. It is not hard to define the
> derivative of FractionalPart as 1, and this is a.e. correct, that is,
> correct except at jumps, where the derivative, strictly speaking, is not
> defined. So a question to ask is what do you want the derivative to do
> at such points? Your gPaper, shown below, will give an Indeterminate at
> x = 12 (which one might regard as a good thing). So if that is the
> behavior you want, well and good.
>
> f[x_] := x^5
>
> Fr[x_] := 1/2 - ArcTan[Cot[Pi*x]]/Pi
>
> gPaper[x_] := Fr[f[x]]
>
> If we simply do
>
> Derivative[FractionalPart][x_] := 1 + DiracDelta[x-IntegerPart[x]]
> Derivative[n_Integer /; n>1][FractionalPart][x_] := 0
>

Will the above two definitions change the behaviour of FractionalPart
function?

> gMath[x_] := FractionalPart[f[x]]
>
> we'll get an exact result for gMath''[61/5] that agrees with yours
> numerically but is in vastly simpler form. We'll also get a rational
> result for gMath'' that might or might not be what you'd want.

Is that really simpler??!! Moreover, you rather used an exact rational
form and you didn't use the approximate 12.2`400 (12.2 correct to 400
digits) to see what my experiment will be? Again, you should use my
definition for FractionalPart function to get precise results.

Now why you used [x-IntegerPart[x]]? Why didn't you simply use
FractionalPart? I will do experiments again, and will post results.. I
hope moderator wont take long to publish them.

Mohamed Al-Dabbagh

```

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