[R] Simultaneous equations

[Peter Dalgaard]

On 09/02/2010 09:25 PM, benhartley903 wrote:
> 
> Dear all, 
> I am relatively new to R and have had some difficulty in understanding the
> user manual for a package that I have downloaded to evaluate non-linear
> simultaneous equations. 
> The package is called systemfit. 
> Does anyone have any experience of this package? 
> What I am trying to do is solve a non linear simultaneous equations... 
> 
> Could anyone give me an example (please) of the code that would be needed to
> return solutions for the following system using systemfit (or any other
> better package): 
> 
> y=1/x 
> y=sin(x) 
> 
> within a range of say x=-10 to 10 (x in radians) 
> 
> Thanks, I really appreciate your help in advance. 
> 
> Ben 

Systemfit is not even in the same ballpark...!

I'd just rewrite the above as

x * sin(x) - 1 = 0

make a graph to bracket the roots and then use uniroot.

> f <- function(x) x*sin(x)-1
> curve(f, interval=c(-10.10)
> f(c(0,2,5,7,10))
[1] -1.0000000  0.8185949 -5.7946214  3.5989062 -6.4402111

So the roots are

> uniroot(f,interval=c(7,10))$root
[1] 9.317241
> uniroot(f,interval=c(5,7))$root
[1] 6.43914
> uniroot(f,interval=c(2,5))$root
[1] 2.772631
> uniroot(f,interval=c(0,2))$root
[1] 1.114161

and 4 more symmetrically below zero.

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com