cancel
Showing results for
Did you mean:
cancel
Showing results for
Did you mean:

Community Tip - Did you get called away in the middle of writing a post? Don't worry you can find your unfinished post later in the Drafts section of your profile page. X

21-Topaz II

## Solving two simple ordinary differential equations with odesolve. Why the second one fails?

Hi all!

Maybe I'm losing in a glass of water, but I can not solve the second differential equation with odesolve, in the problem hereunder exposed. What's wrong?

1 ACCEPTED SOLUTION

Accepted Solutions
13-Aquamarine
(To:-MFra-)

Dear F.M.,

Viktor

Viktor
9 REPLIES 9
13-Aquamarine
(To:-MFra-)

Hi F.M.

I'm missing the equation Fy(x) in the solver.

(or is it F0y(x)?) if yes, i got this solution:

is this right?

Best Regards, Volker

Volker
21-Topaz II
(To:vlehner)

Thanks Volker,

This is a basic case and I need to check out the results.

In the general case, the analytical solution of the first equation is not known. It is used in the second where the problem arises.

Greetings

Frank

13-Aquamarine
(To:-MFra-)

Hi Frank,

And the answer is sooooooo easy with the choice of Adaptive mode.

You can keep your sheet like it was in the origin and change only to adaptive and it works perfectly.

Viktor is absolutely right.

Man lernt nie aus....

Greetings, Volker

Volker
13-Aquamarine
(To:-MFra-)

Dear F.M.,

Viktor

Viktor
21-Topaz II
(To:ViktorKorobov)

Hi Viktor,

thank you very much.

Greetings

Frank

13-Aquamarine
(To:-MFra-)

Frank, I was glad to help. But I do not know why Adams/BDF-method not work here.

Viktor

Viktor
21-Topaz II
(To:ViktorKorobov)

This is not clear to me as well. Let's wait and see if there is someone who will tell us about it.

Frank

24-Ruby V
(To:-MFra-)

At least I can explain whats going on (but not exactly why its going on 😉

Both odesolve-block should solve for x from 10^-6 up to 4*10^-6.

But the second block calls the first and already  in the 15th try the adamsBDF feeds x=4.34*10^-6 inF.y(x) which makes the first solve block fail because that value is grater than the upper limit 4*10^-6.

Attached are the x-values used by AdamsBDF and Adaptive (the latter is truncated as i did not want to wait for all the writing to finish).

If you trap that error, you can also use AdamsBDF in your second solve block:

21-Topaz II
(To:Werner_E)

Thank you very much, Werner.

Franc

Announcements
Top Tags