R help - Sep 2009 - NLM

I am trying to understand NLM package, so I generated this data set consisting y
and x using

y= a + b*x +c*x^2 + N(0,10), with a=3.5,b=4.5,c=5.5


Given y and x, I am trying to use NLM to have estimates of parameters a, b and c
that minimize the least square error

my code looks like
 
f<- function(y,x,a,b,c) {sum((y-(a+b*x+c*x^2))^2)}
nlm(f, y, x, a=3, b=4,c=5)


But it comes up with rediculous result. My understanding of this NLM must be
wrong.

Please help!

Andy

Andrew Wang wrote:
> I am trying to understand NLM package, so I generated this data set
consisting y and x using
> 
> y= a + b*x +c*x^2 + N(0,10), with a=3.5,b=4.5,c=5.5
> 
> 
> Given y and x, I am trying to use NLM to have estimates of parameters a, b
and c that minimize the least square error
> 
> my code looks like
>  
> f<- function(y,x,a,b,c) {sum((y-(a+b*x+c*x^2))^2)}
> nlm(f, y, x, a=3, b=4,c=5)
> 
> 
> But it comes up with rediculous result. My understanding of this NLM must
be wrong.


See ?nlm for the arguments you have to pass to nlm() and how the 
function needs to be written. There are also some examples on that help 
page.

Uwe Ligges


> Please help!
> 
> Andy
> 
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