Exact Differential Equations of Order n?

Click For Summary

Discussion Overview

The discussion revolves around the concept of exact differential equations, particularly in the context of second order ordinary differential equations (ODEs). Participants explore the relationship between higher order ODEs and first order exact equations, referencing historical texts and theorems related to the topic.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant presents a second order ODE and questions how to analyze it in terms of exact differential equations, referencing a quote from a historical text.
  • Another participant critiques the referenced text for lacking a clear definition of "exact" equations and suggests it may not be a helpful resource.
  • A third participant defends the text, noting its historical significance and expressing surprise at the dismissal of its content, while also suggesting that the definition of exactness should be treated as a theorem.
  • A later reply clarifies that no insult was intended in the previous comments and acknowledges the difficulty in providing a definitive answer to the original question.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the usefulness of the referenced text or the clarity of the definitions provided. There are competing views on the interpretation of exactness in the context of higher order ODEs.

Contextual Notes

The discussion highlights the complexity of linking higher order exactness with first order exactness, and the varying interpretations of historical texts on the subject. There is an acknowledgment of the limitations in definitions and the potential for differing understandings among participants.

bolbteppa
Messages
300
Reaction score
41
A second order ode Py'' + Qy' + Ry = 0 is exact if there exists a first order ode Ay' + By such that

(Ay' + By)' = Ay'' + (A' + B)y' + B'y = Py'' + Qy' + Ry = 0

How can one cast the analysis of this question in terms of exact differential equations?

In other words, could somebody explain this interesting quote:

The derivation of the conditions of exact integrability of an ordinary differential equation of the nth. order (or of a differential expression involving derivatives of a single dependent variable with regard to a single independent variable) is sometimes made to depend upon the theory of integration of an expression, exact in the sense of the foregoing chapter. As however the connection is not immediate and this method is not the principal method, it will be sufficient here to give the following references to some of the writers on the subject, in whose memoirs references to Euler, Lagrange, Lexell, and Condorcet, will be found in ...
Forsyth - Page 33

Thanks!
 
  • Like
Likes   Reactions: 1 person
Physics news on Phys.org
exact in the sense of the foregoing chapter
... see foregoing chapter.
(reads) seems the author launches into investigating "exact" equations without making a general definition.
That's a pretty nasty text btw. I'd be remiss if I didn't advise you to ditch it.

For an idea how the concept of "exactness" may apply to higher order ODEs see instead:
http://reference.wolfram.com/mathematica/tutorial/DSolveExactLinearSecondOrderODEs.html
 
That doesn't help, neither the insult nor the link, but thanks...

The book does Frobenius' theorem in like a page, & spends hundreds of pages on inexact equations & is filled with history as well as substance, I'm surprised anyone with any appreciation for such a subject would write something like this off so easily. Also, the definition you've provided should really be a theorem if we're trying to link higher order exactness with first order exactness, but how and ever...
 
Last edited:
  • Like
Likes   Reactions: 1 person
Sorry - no insult intended.
Please note that I have not provided any definitions.
If the text works for you then that is great and I'm sure you'll figure out what the author is talking about in due course.

However, I don't think I can provide the answer in the form you are looking for.
I'll see if I can attract someone else.
Cheers.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 52 ·
2
Replies
52
Views
8K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 19 ·
Replies
19
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K