R help - Dec 2011 - simple fit

Dear all,
 I have a formula of the form
y=ax+b
I know everything except b. How I can ask R to do fitting to find only the value
of b?
I already know the lm() but it always return both an intercept point (b) and the
a.

What should I do ?

I would like to thank you in advance for your help

B.R
Alex

	[[alternative HTML version deleted]]

Fit y-b without an intercept? (which you do by adding "+ 0" or "-
1"
to the model formula) Not sure if this is the optimal result, but it
will give you a pretty reasonable answer.

Michael

On Thu, Dec 8, 2011 at 10:52 AM, Alaios <alaios at yahoo.com>
wrote:
> Dear all,
> ?I have a formula of the form
> y=ax+b
> I know everything except b. How I can ask R to do fitting to find only the
value of b?
> I already know the lm() but it always return both an intercept point (b)
and the a.
>
> What should I do ?
>
> I would like to thank you in advance for your help
>
> B.R
> Alex
>
> ? ? ? ?[[alternative HTML version deleted]]
>
>
> ______________________________________________
> R-help at r-project.org 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.
>

R. Michael Weylandt <michael.weylandt <at> gmail.com> writes:
> Fit y-b without an intercept? (which you do by adding "+ 0" or
"- 1"
> to the model formula) Not sure if this is the optimal result, but it
> will give you a pretty reasonable answer.
 This seems backward.  The OP has the slope and wants the intercept.
> On Thu, Dec 8, 2011 at 10:52 AM, Alaios <alaios <at> yahoo.com>
wrote:
> > ?I have a formula of the form
> > y=ax+b
> > I know everything except b. 
> > How I can ask R to do fitting to find only the value of b?
> > I already know the lm() but it always return both an intercept point
> >  (b) and the a.
 Or:

  lm (y~1,offset=a*x,data= ...) 

or

  lm(y-a*x~1,data=...)  [not sure this will evaluate the full
expresson on the LHS but it might]

If one knows y, x, and a, and wishes to estimate b in

     y = a*x + b (+ random error presumably)

then surely the simplest procedure is

     b.hat <- mean(y-a*x)

Is it not so?

     cheers,

         Rolf

On 09/12/11 08:09, Ben Bolker wrote:
> R. Michael Weylandt<michael.weylandt<at>  gmail.com>  writes:
>
>> Fit y-b without an intercept? (which you do by adding "+ 0"
or "- 1"
>> to the model formula) Not sure if this is the optimal result, but it
>> will give you a pretty reasonable answer.
>   This seems backward.  The OP has the slope and wants the intercept.
>
>> On Thu, Dec 8, 2011 at 10:52 AM, Alaios<alaios<at> 
yahoo.com>  wrote:
>>>   I have a formula of the form
>>> y=ax+b
>>> I know everything except b.
>>> How I can ask R to do fitting to find only the value of b?
>>> I already know the lm() but it always return both an intercept
point
>>>   (b) and the a.
>   Or:
>
>    lm (y~1,offset=a*x,data= ...)
>
> or
>
>    lm(y-a*x~1,data=...)  [not sure this will evaluate the full
> expresson on the LHS but it might]
>
> ______________________________________________
> R-help at r-project.org 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.