Re: [R] need suggestion about building formual

From: Spencer Graves <>
Date: Wed 12 Oct 2005 - 10:54:43 EST

          Have you considered writing a function to do the complex math and then calling nls referring to that function? Consider the following (not tried):

expg <- function(a., x, G0, R, T){


mynls<-nls(formula=y~expg(a.=c(a, b), x=x, G0=G0, R=R, T=T),


          If "nls" stops prematurely, I then write another function, "SSE" to compute the sum of squares of deviations from y and then ask "optim" to minimize "SSE", using "hessian=TRUE". If you try this and have trouble making it work, please send another post.

          spencer graves

Simple wrote:

> Thanks for your kind respond. Although the answer didn't solve my question
> clearly,maybe I still not understand the art of R.
> I'm sorry that I had not talked the problem clearly, maybe a example with more
> detail will be suitable as suggested in the the posting guide.
> In function fitting program, such as Sigmaplot, a fitting formula, can be
> write in separate form:
> G=a+(b*x)^(1/2)
> k=exp((G-G0)/(R*T))
> fit k to y
> of course,in R's nls, can write as:
> mynls<-nls(formula=y~exp((a+(b*x)^(1/2)-G0)/(R*T)),data=mydata,...)
> In this example, the formula is simple and acceptable. However, when the
> formula is more complexity,writing all in one formula,the readability will be
> damaged.So I'm looking for a way to write simple and readable code in this
> situation.
> Spencer Graves wrote:

>>	  I'm not certain what you are asking.
>>	  You can build expressions in R as character strings and then execute
>>them.  Example:
>>expr <- paste("two <-", 1, "+", 1)
>>	  If this does not answer your question, PLEASE do read the posting
>>guide, "".  It can help increase the
>>chances of a quick and useful reply.
>>	  spencer graves
>>Simple wrote:
>>>I'm an newbie for R,I want do some fitting in R.
>>>I wander if it is possible to write a few of equations but only one
>>>formual when fitting
>>>Currently,My problem is,in R, is there methods combination a few
>>>equations into one formual?
>>>For example,
>>>although it is certain that the can be equations turn into one formual as
>>>y~f(x),but write such a complexity string make me painful.
>>>I have searched the web and found out there were only examples with one
>>>formual.any suggestion?
>>>I hope that I have omit something.

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Spencer Graves, PhD
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Received on Wed Oct 12 11:08:56 2005

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