16 Replies Latest reply: Nov 27, 2013 2:45 AM by WalterSchrabmair

# Laplace and ODE - what is wrong?

Dear friends,

I have here a simple example, but in MC15 I do not get the same results as in the example.

WHo can help?

Thanks

Walter

• ###### Re: Laplace and ODE - what is wrong?

I have found my misunderstanding of Laplace transform. Only f(t) must be tranformed, see MC15 sheet.

• ###### Re: Laplace and ODE - what is wrong?

Do you know this:

• ###### Re: Laplace and ODE - what is wrong?

Dear Valery,

I want to solve a ODE by LaplaceTransformation. I have f(t) and in MMA the results is as follows. (see pic)

ANd in MC 15 I do get a other form. Is that the same? Thanks for help

Walter

• ###### Re: Laplace and ODE - what is wrong?

Here I could solve the ODE with laplace in MMA successfully. BUT in MC it does n ot work .

Thanks

Walter

• ###### Re: Laplace and ODE - what is wrong?

Mathcad is primarily a numeric calculator; the symbolic processor, while convenient, is not always as good as we'd like.

Accepting some help from the books and literature allows us to do the laplace transform of the Heaviside function by ourselves:

Can you solve it then?

• ###### Re: Laplace and ODE - what is wrong?

Dear Fred,

thanks a lot for your fast response.

When I transform the f(t) with MMA I got this result. Are you sure that you did not miss the Theta(-tau)?

• ###### Re: Laplace and ODE - what is wrong?

There is (was) a lot of errors at Laplace Trans in Mathcad 14/15 (with MuPad not Maple Symbolic Engine).

• ###### Re: Laplace and ODE - what is wrong?

I'm flailing a bit, and my version 14.0 is having serious problems with the symbolic solver.

See if this makes sense:

• ###### Re: Laplace and ODE - what is wrong?

Looks good but got still an error that the X1 or X2 fn is not defined - even that in MC 15 the red invlap lines signals that is just to big to display but should be able to store in fn.

Thanks a lot

• ###### Re: Laplace and ODE - what is wrong?

THis Problem with Laplace substitution can also not be solve in MathCAD 15 M 020. WHat a shame!

• ###### Re: Laplace and ODE - what is wrong?

The real problem seems not to be that the expression is too big but rather that Mathcad simply is not capable of doing that specific inverse Laplace transform. After definition of all variables the expression is not too big anymore but nevertheless useless.

I agree - it's a shame

• ###### Re: Laplace and ODE - what is wrong?

Thanks Werner, yes I agree to you. Let`s wait until PRIME 6.0, maybe they will correct this bug.

• ###### Re: Laplace and ODE - what is wrong?

Prime 6 already!? Thats what I call optimism and positive thinking ;-)

But then, I won't bet on it.