non-linear fourth-order differential equations

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non-linear fourth-order differential equations

Yanika Borg
I need to solve a system of non-linear fourth-order differential
equations. Is there a command which solves this system?

Thanks in advance.

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Re: non-linear fourth-order differential equations

Wu Gong
Hi Yanika,

Please try ?uniroot and ?ployroot

f <- function(x) x^4-16
uniroot(f, lower= -3, upper=0)
polyroot(c(-16,0,0,0,1))
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Re: non-linear fourth-order differential equations

Ravi Varadhan
OP is asking about a system of fourth-order "differential" equations,
whereas you are telling her how to solve a single, algebraic nonlinear
equation.

Take a look at package "deSolve", and the function `lsode' in that package
for solving a system of nonlinear ODEs (given initial values).

Ravi.

-------------------------------------------------------
Ravi Varadhan, Ph.D.
Assistant Professor,
Division of Geriatric Medicine and Gerontology School of Medicine Johns
Hopkins University

Ph. (410) 502-2619
email: [hidden email]

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Wu Gong
Sent: Sunday, November 28, 2010 6:31 PM
To: [hidden email]
Subject: Re: [R] non-linear fourth-order differential equations


Hi Yanika,

Please try ?uniroot and ?ployroot

f <- function(x) x^4-16
uniroot(f, lower= -3, upper=0)
polyroot(c(-16,0,0,0,1))

-----
A R learner.
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View this message in context:
http://r.789695.n4.nabble.com/non-linear-fourth-order-differential-equations
-tp3062805p3062894.html
Sent from the R help mailing list archive at Nabble.com.

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Re: non-linear fourth-order differential equations

Wu Gong
Hi Ravi,

Thank you for your correction. I hope I didn't mess up anything:)

Cheers.

Wu
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Re: non-linear fourth-order differential equations

Karline
In reply to this post by Yanika Borg
Hi Yanika,

Depending on whether your problem is an initial value problem or a
boundary value problem, you can find solution methods in R-packages
deSolve (IVP) and bvpSolve (BVP).

The solvers in deSolve only solve differential equations written in
first-order form; bvpSolve can handle higher-order DEs.

For use in deSolve, you need to rewrite the 4th order DE as a set of 4
first-order equations:
d''''y /dt = f(t,y) then becomes:
dy1 = y2; dy2 = y3; dy3 = y4; dy4 = f(t,y)

Hope this helps,


Karline

Message: 32
Date: Sun, 28 Nov 2010 22:47:59 +0100
From: Yanika Borg <[hidden email]>
To: [hidden email]
Subject: [R] non-linear fourth-order differential equations
Message-ID:
        <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1

I need to solve a system of non-linear fourth-order differential
equations. Is there a command which solves this system?

Thanks in advance.

______________________________________________
[hidden email] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
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Re: non-linear fourth-order differential equations

Thomas Petzoldt
Hi Yanika,

more information about deSolve (books, papers, tutorials) can be found
on the deSolve homepage:

http://desolve.r-forge.r-project.org

and, of course, in the package documentations. If you need further help
from the list, please provide a short reproducible example.

Thomas Petzoldt


--
Dr. Thomas Petzoldt
Limnology and Ecological Modelling

Technische Universitaet Dresden
Fakulty of Forest, Geo and Hydro Sciences
Institute of Hydrobiology
01062 Dresden, Germany
E-Mail: [hidden email]
http://tu-dresden.de/Members/thomas.petzoldt

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