Get Help

Turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- Community
- :
- PTC Mathcad
- :
- PTC Mathcad
- :
- Re: Nonlinear 1°ord differential equation

Options

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Mute
- Printer Friendly Page

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-17-2018
01:10 PM

09-17-2018
01:10 PM

Hi everybody,

how can I solve this equation?

I found problems because of the derivative function squared. I need to collect the term derivative not squared...

Thanks

Bye

Solved! Go to Solution.

Labels:

1 ACCEPTED SOLUTION

Accepted Solutions

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-18-2018
04:09 AM

09-18-2018
04:09 AM

You can turn the non-linear y'(t)^2 + 4y'(t) = 5ty(t) into two simultaneous linear ode's:

Alan

9 REPLIES 9

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-17-2018
01:16 PM

09-17-2018
01:16 PM

Re: Nonlinear 1°ord differential equation

Hmm squared.... Seems more like to the 3rd power.

You have (y'(t))^2 and mutiply that with 4 y'(t), that gives 4*(y'(t))^3...

Do you need a symbolic solution, or can you settle for a numeric approximation.

Either way: what are the initial values? [ y(0), y'(0)]

Luc

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-17-2018
01:22 PM

09-17-2018
01:22 PM

Re: Nonlinear 1°ord differential equation

Found it.

Try y(t)=+/-(1/8)*sqrt(10)*t^2.

The third solution is y(t)=0, but I guess you weren't looking for that.

Success!

Luc

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-17-2018
01:30 PM

09-17-2018
01:30 PM

Re: Nonlinear 1°ord differential equation

Here's a possible workaround for a numerical solution, both Prime and real Mathcad:

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-17-2018
06:39 PM

09-17-2018
06:39 PM

Re: Nonlinear 1°ord differential equation

I'm so sorry because I wrote "(y'(t)^2) ***** 4y'(t)" instead of "(y'(t)^2) **+** 4y'(t)" that it changes a lot...

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-17-2018
07:11 PM

09-17-2018
07:11 PM

Re: Nonlinear 1°ord differential equation

From Mathcad's documentation of "odesolve":

The ODE must be linear in its highest derivative term,

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-18-2018
01:01 AM

09-18-2018
01:01 AM

Re: Nonlinear 1°ord differential equation

Does y(t) describe a physical phenomenon as a function of time? Or is this a made-up DE?

Luc

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-18-2018
04:09 AM

09-18-2018
04:09 AM

You can turn the non-linear y'(t)^2 + 4y'(t) = 5ty(t) into two simultaneous linear ode's:

Alan

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-19-2018
05:18 AM

09-19-2018
05:18 AM

Re: Nonlinear 1°ord differential equation

How to find y(0)=1?

z(0)=0, How about z(0)=-4?

Tokoro.

Highlighted
##

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

09-19-2018
06:03 AM

09-19-2018
06:03 AM

Re: Nonlinear 1°ord differential equation

y(0)=1 was an arbitrary choice on my part, as no initial conditions were specified in the original question.

z(0)=-4 gives rise to a rapidly decreasing y with time (and with y(0)=1). If this is what is expected from the model then fine! Personally, I think it’s probably safer to stick with z(0)=0.

Alan