Help with Complex Polynomial equation in mathematica

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Discussion Overview

The discussion revolves around the challenges of analyzing complex polynomial equations in Mathematica, specifically in the context of electronic filter design. Participants explore issues related to obtaining the norm (or modulus) of complex numbers, plotting functions, and manipulating expressions symbolically.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in obtaining the norm of a complex polynomial using variables in Mathematica, noting that functions like Norm[] and Re[] do not yield the expected results.
  • Another participant suggests that the term "norm" may be confused with "abs" and emphasizes the importance of using the correct functions for simplification and plotting.
  • A participant seeks clarification on how to obtain the norm of a complex number without fixed values, providing an example that illustrates their expectations.
  • Some participants discuss the appropriateness of focusing on symbolic manipulation versus direct plotting, with differing opinions on the necessity of obtaining a specific symbolic form for plotting purposes.
  • A later reply mentions the potential for Mathematica to hang when using the Abs[] function in conjunction with plotting, suggesting that the Manipulate[] function may be a contributing factor.
  • Another participant expresses a desire to understand the theoretical aspects of filter design rather than just plotting results, indicating a focus on the manipulation of complex equations.
  • One participant suggests using FullSimplify or ComplexExpand to simplify expressions, questioning whether these methods were attempted by the original poster.
  • The original poster acknowledges their inexperience with Mathematica and expresses gratitude for the assistance received.
  • Later in the thread, the original poster introduces a new problem related to running a Laplace equation and seeks further help.

Areas of Agreement / Disagreement

Participants exhibit a mix of agreement and disagreement regarding the best approach to manipulating complex expressions and plotting in Mathematica. Some advocate for a focus on plotting without symbolic manipulation, while others emphasize the importance of understanding the underlying mathematical relationships.

Contextual Notes

Limitations include the original poster's inexperience with Mathematica, which may affect their ability to utilize certain functions effectively. There is also uncertainty regarding the specific methods that have been tried or not tried in simplifying expressions.

Who May Find This Useful

This discussion may be useful for individuals learning to use Mathematica for complex analysis, particularly in the context of electronic filter design and those seeking to understand the manipulation of complex expressions.

Don Diego
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Hi everybody:
I'm trying to analyse equations of analogue electronic filters, but i can't get the "norm" of the complex polynom if i use variables (or symbols? what's the difference?), here's the simplest exemple (RC low pass filter, a represents R*C*w, reals variables > 0):

Assuming[ a \[Element] Reals && a > 0, Norm[1/(1 + a \[ImaginaryJ])]]

Norm[1/(1 + I a)]

The answer :

Norm[1/(1 + I a)] ----- the same thing!

Re[] and Im[] doesn't work either!
I will like to uses to find the argument (Arg[] doesn't work)

and after all, make my bode plots!
please help me, I'm new in mathematica!
Thanks
 
Physics news on Phys.org
up?? somebody?? help!
 
Norm? Do you mean Abs?

If you want it to try and simplify things, or expand a function, or other stuff, you should invoke the appropriate functions...

And if you want to plot something, just plot it. If it evaluates to a real number, it doesn't matter what the symbolic form is.
 
Hi Hurkyl, and thanks for the answer:

My problem is that i can't get the "modulus" or "norm" of the Complex number, once i get the norm (norm = abs) i would like to plot it as a fonction of "w", how can i get the Norm of à complex number without fixed values??
exemple:
Norm[1/(1 + 3 \[ImaginaryJ])]
then i get :
1/Sqrt[10]

with Norm[(1/(1 + a \[ImaginaryJ]))
i get Norm[(1/(1 + a \[ImaginaryJ])), the same thing!

i should get : 1/(\[Sqrt]1 + a^2)
... what ca i do?
 
What part of my response didn't you understand?
 
Yeah, it's a drag…
For your particular example, this gives the appropriate result :

http://img185.imageshack.us/img185/319/picture1qs.jpg

I suggest you define a function which does the above :biggrin:
 
Last edited by a moderator:
GREAT GREAT! I'm going to try this! Thanks so much gueromm00! you are great!
I'm going to put my results with à more complex filter!
:):):)! thanks!
 
Voila Voila!
RLC Low pass filter in the attachement!
thanks a lot!
 

Attachments

  • RLC Mathematica.jpg
    RLC Mathematica.jpg
    42.2 KB · Views: 585
Why are you bothering trying to coerce Mathematica to express it in a particular symbolic form when all you really want to do is plot it?
 
  • #10
Hurkyl said:
Why are you bothering trying to coerce Mathematica to express it in a particular symbolic form when all you really want to do is plot it?

Well, in my case at least, when simply using the Abs[] function Mathematica hangs when trying to plot…
So, it does make sense to help him a little :smile:
I think it is because of the Manipulate[]… (otherwise, I agree with you : since all plots functions have an HoldAll attribute, it doesn't matter what symbolic form its argument evaluates to)
 
Last edited:
  • #11
This was just un exemple, what i really want to do it's to manipulate the complex expressions in a theorycal way, I'm learning about filters ok?, i don't want to just plot something without understanding the original relation. my problem was just about the manipulation of complex equations and now it's OK.
Thanks guerom00, you're really nice! :biggrin:
:cool:
 
  • #12
That's fair. It's hard for me to tell, since you didn't really respond to any of my earlier comments. :frown:

I am mildly surprised that you cannot just FullSimplify your original expression (with an assuming clause), or possibly ComplexExpand it. Or... was that just not tried? Ah well, I forgot to play with it earlier when I had a chance.
 
  • #13
Sorry Hurkyl, but I'm new in mathematica, i didn't know about "complexexpand"... i think that you didn't realize that I'm a newbie, i don't understant everything about mathematica, thanks for yours comments ;)
 
  • #14
Hi!
Now i have one new problem, i can't run this Laplace equation (see attachement)

I don't know what to do, sorry... please help me!
Thanks!

See the "InverseLaplaceTransform" don't show me the answer... why?
 

Attachments

  • Laplace problem.jpg
    Laplace problem.jpg
    30.9 KB · Views: 604
  • #15
When I made my reply, I was keying in on your desire to plot, which doesn't require manipulating things into a "nice" form. I was hoping that if you were less interested in plotting and more interested in "simplifying things" or "expand a function"... or that it would prompt you to look up the keywords "simplify" or "expand" in the help.

Have you looked through Mathematica's documentation center? (e.g. under the "help" menu, or by hitting F1 after highlighting a word) It's pretty good. I didn't know about ComplexExpand myself, but I expect it's not hard to find if you started with the page for Expand or Simplify. I think there's even an article on "simplifying functions" but it's been a while since I looked at it.
 

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