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GabrielM8
Level 3
37 24 1 5
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How to get complex partial fractions in HP Prime?

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I'd like to get the result below using partial fractions (directly) in HP Prime.

 

 

fractions.png

 

I'v tried use partfrac() but it does not show complex results.

Maybe using another function, we can get the image result.

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Ciro_Bruno
Level 4
137 122 6 17
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Hello Gabriel

 

You might have left Complex numbers option unchecked. Please take a look at CAS Settings:

 

01.png

 

I've checked your denominators to know better what to expect in the partial fractions:

02.png

 

Then I've typed in your sentence. Nevertheless, I've got for result sometinhg containing "rootof". Here you are some parts of its giant result:

 

03a.png03b.png03f.png03r.png

 

 

Honestly, I have no idea what that "rootof" means in terms of solution. FOR ME IT'S GOOD FOR NOTHING !!!

It goes against any expectation I could have on a product of HP Prime category. 

 

Anyway, I've tried also a simpler expression, with smaller roots in denominator. The result, after approximation looks "readable".

04a.png04b.png

 

This is something I would expect from HP Prime. Unfortunatelly it doesn't work like that every time.

 

We've already faced troubles with partfrac recently, which have been corrected by the latest update.

Problem with partfrac on HP Prime

I hope we'll soon have the next improvement to get this example solved as well.

 

In case of any update, please let us know.

Regards,

Ciro.

 

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Maké
Level 9
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Message 3 of 15
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Hi!, @Gabriel8 :

Can you explained better each variable equation's and where you needed use ?.

Kind Regards !.
Have a nice day !.
@Maké (Technical Advisor Premium - HP Program Top Contributor).
Provost in HP Spanish Public Forum ... https://h30467.www3.hp.com/
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GabrielM8
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That is partial fraction, i need it to calculate inverse laplace transform:

                                             iL(s) -> iL(t)
I know how to calculate manually but I'd to know how can i set to HP Prime give me the right answer (directly).

 

By the way, neither the function ilaplace() give me the right answer of this inverse laplace transform.

Here is the answer of inverse laplace transform from "Circuitos Eletricos - 10ª edição - Nilsson Riedel" (BOOK):

 

ilaplace.gif

 

Let me know if you can get this answer directly from HP Prime.

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Maké
Level 9
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Hi!, @GabrielM8 :

See, the result of Inverse Laplace, with Wolfram Alpha ... https://www.wolframalpha.com/input/?i=inverse+laplace((100*s%5E2)%2F((s%5E2%2B1500*s%2B10%5E6)*(s%5E...))

In comparision with HP PRIME, with ilaplace the result mybe is same (approximate mode)

Kind Regards !.
Have a nice day !.
@Maké (Technical Advisor Premium - HP Program Top Contributor).
Provost in HP Spanish Public Forum ... https://h30467.www3.hp.com/
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Ciro_Bruno
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Hello Gabriel

 

Maybe you can get the result directly with iLaplace itself. But remember you have to declare both Laplace variable ("s") and the target time variable ("t") by appending ",s,t" as last arguments. Please take a look:

 

05 iLaplace a.png

 

But, again, you may not obtain "readable" result. Again I'd say it's good for nothing such answer and you won't manage to understand your circuit by this answer.

 

So, take it, as it is, and operate "collect(expand(weird expression)". Then you get:

05 iLaplace b.png

Please, if someday you find something to replace collect(expand()), please let me know. I've already tried.

[HP Prime] expand(collect(...)) Is there any better way?

 

Last but not least, I see you've been using angles in Degrees as well as in Radians. Maybe you've been doing the same with frequencies. I can see decimal frequency in one member and 120pi (=60Hz) in the same expression you have phase angle in degrees. Be carefull. You must calculate any time depending oscilation funcion in Radians. Maybe the book you're using explores each concept in its singular way, in order to help the reader to understand it better. Maybe the writer assumes that there's no need to detail the resolution paths. In this case, you'll have to tidy the expression before stepping forward.

 

I hope it helps.

Regards,

Ciro.

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GabrielM8
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37 24 1 5
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Interesting technique Ciro Bruno! Thanks!

 

But I did not get the same result as on your calculator, maybe my settings are wrong (I did not understand what some options still work) as you can see in the images below. Can you show which settings you use?

 

1.gif

 

2.gif

 

 

 

Thanks for the warning about the units. Actually my book does not explain many details about the units. So the result of this function will be in radians, and I have to change to degrees later (if I need)?

 

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Ciro_Bruno
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Hello Gabriel

 

Later I'm gonna take a carefull look at your results and try to find out configuration issues. Which software version have you been using in your prime?

 

When I tell you about converting everything to Radians, I mean you've got to do it on the paper. Before you transform it into Laplace. Later, as you transform it back to time funcion and you want to compare results between from calculator and books, make sure that your book is giving you an units coherent equation. If not, you have to convert them. Remember that, most likely, the author hasn't used a calculator.

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GabrielM8
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I'm using firmware 20181016.

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Maké
Level 9
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Hi!, @GabrielM8 :

You can check the ultimates, from ... ftp://ftp.hp.com/pub/calculators/Prime

Kind Regards !.
Have a nice day !.
@Maké (Technical Advisor Premium - HP Program Top Contributor).
Provost in HP Spanish Public Forum ... https://h30467.www3.hp.com/
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