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Newbie

hi there.

i got some problems in mathcad(a new user) regarding laplace (err. inverse laplace) transforms

browsing the net, i got some exercise for mathcad: http://www.unf.edu/~mzhan/chapter6.pdf

problem arises when i tried to get the inverse laplace of 8a*s^2/(s^2+a^2)^3..

i didn't get any answer other than mathcad(14) making what i typed to red....

also, when i didn't even get the right inverse laplace of (-(2 a (a^2 - 3 s^2))/(a^2 + s^2)^3))..

the thing is, inverse laplace-ing the laplace of f(t) don't give me f(t)...

mathematica did solved both my problems correctly..

mathcad seem to fail in that aspect?

Tags (2)
9 REPLIES 9

## Re: mathcad errors; inverse laplace

Could you please post a worksheet.

Also, which version of Mathcad are you running, including service releases?

## Re: mathcad errors; inverse laplace

2. Your version of Mathcad is short and lazy in Laplace !

Don't take my word, but it seemed to me that the Mathcad versions above 11 [that aren't Maple ] , Laplace was Carson-Laplace. That's probably why it was so much reported as "bug" in Mathcad-MuPad ! That stuff is few [few = many] years back, and no recollection of Engineering work based on Carson-Laplace. You could check by comparing your result vs a conversion table. As you mentioned Mathematica, version 4.0 is "Laplace".

jmG

## Re: mathcad errors; inverse laplace

I know I used to do Laplace / Inverse Laplace in school all the time back in MathCad 11 and it worked great. After seeing this post, I tried it today in MathCad 14 M030 and I agree with the original poster, I'm not too pleased with the output...

I tried some additional symbolic operators (simplify, collect, etc.) to see if I could "encourage" an output in the form I was looking for....with no luck.

So now I'm off to read about the what changes were made in MathCad that are causing it to be "lazy" (as termed by Jean in the previous post) like this and not produce the result that I would expect (after using MathCad 11 for so many years to do this perfectly).

August

## Re: mathcad errors; inverse laplace

 So now I'm off to read about the what changes were made in MathCad that are causing it to be "lazy" (as termed by Jean in the previous post) like this and not produce the result that I would expect (after using MathCad 11 for so many years to do this perfectly).

Going from MC13 to MC14 the symbolic engine was chnaged from Maple to MuPad. The MuPad engine has very poor integral tables and has problems with integrals, Fourier transforms, and Laplace transforms. Sometimes it can't solve them, sometimes it gets them wrong. Some of this has been fixed, but obviously not all of it.

## Re: mathcad errors; inverse laplace

August,

Mathcad 14 solution reveals the system it is reading is under determined, You could try the partial fraction expansion. If it does not work, the question is: MuPad can it do or should it do ? The answer is: it should but if it can't , then zap.

Jean

## Re: mathcad errors; inverse laplace

I tried it on 15.0.0.436 (trial) and ended up with the same result as August's..

-license says Feature Version 14.1, Version 15.0 Beta

Attached is side-by-side compasion with mathematica...

@Jean

What version of MathCad are you using?

So is it better to downgrade and just use Jean's version?

Thanks a lot.

## Re: mathcad errors; inverse laplace

 @JeanWhat version of MathCad are you using?So is it better to downgrade and just use Jean's version?

Any version prior to 14 will give that result, because they all use the Maple engine. If you downgrade get either MC13 or MC11. Do not get MC12! If you downgrade you may not be able to get Mathcad to run on either Vista or Windows 7.

## Re: mathcad errors; inverse laplace

 Nowel Lubi wrote:I tried it on 15.0.0.436 (trial) and ended up with the same result as August's..-license says Feature Version 14.1, Version 15.0 BetaAttached is side-by-side compasion with mathematica...@JeanWhat version of MathCad are you using?So is it better to downgrade and just use Jean's version?Thanks a lot.

What's the use of Win 7, Vista ? I use Excel to draw lines, and little more gadgets, Paint [a lotlotlot], NotePad [a lot too].

What's the use of Win 7 32 decimals ln(1.23456789) ? If you have Win 7 and Mathematica, ask Mathematica what is your "Machine precision" , if it replies 16, then no numerical maths will take or exploit 32 decimals,

Jean

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## Re: mathcad errors; inverse laplace

thanks a lot jean.

thank you guys (and gals), also, for those insights and replies..

Good day!

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