R help - Oct 2012 - summation sign

Hi all,
I have a very quick question on how to use the summation sign in R for the
function.
Here?s a basic example: the function is sum(i=1 to 5)log(1-xi^2)
Id be grateful if someone knows how to do this without writing it out 5
times - I am looking sth along the lines of  the following:

computeR <- function(x)
  {
    return (-sum(log(1-x^2))
}^
thank you vm in advance!



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On Oct 27, 2012, at 01:34 , sffarooqi wrote:
> Hi all,
> I have a very quick question on how to use the summation sign in R for the
> function.
> Here?s a basic example: the function is sum(i=1 to 5)log(1-xi^2)
> Id be grateful if someone knows how to do this without writing it out 5
> times - I am looking sth along the lines of  the following:
> 
> computeR <- function(x)
>  {
>    return (-sum(log(1-x^2))
> }^
> thank you vm in advance!
You pretty much did it already:
> x <- c(.5,.6,.7,.4,.8)
> -sum(log(1-x^2))
[1] 2.603318

I.e., just have x as a vector of length 5 and the rest is done automagically.

(And, BTW, you don't need return() in a function like that in R, the return
value is the value of the last expression.)

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

thank you vm for the reply! Just to make things a little more complicated
--does the equation hold even if the values of x are unknown? More
specifically perhaps we can still refer to the made up example 
Sum(n equal 5)log(1-xi^2) 

In the problem I am working on, I am writing a modified Newton Optimisation
code with linesearch. Therefore the values of x are not given but each x
variable is some nx1 vector ..e.g. lets take a 3x1 vector. 
So referring to this example, where we had to sum 5 times, how could I write
the function such that it sums 5 times, but each of the 5 x variables is
taken to be a 3x1 vector.  

thank you very much again!




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Hi Sara,

Not very clear either.

You mentioned you want to repeat the sum 5 times.? Is it on the same x variable
or different x variables?
If you want to repeat the sum 5 times on the same x variable,

x1<-c(.3,.2,.1)
?fun1<-function(x,i){
?res<-lapply(1:i,function(y) -sum(log(1-x^2)))
?res1<-unlist(res)
?res1}
?fun1(x1,5)
#[1] 0.145183 0.145183 0.145183 0.145183 0.145183

But, if you want? to do the sum on different vector of same or different length

x1<-c(.3,.2,.1)
?x2<-c(.5,.6,.1)
?x3<-c(.1,.6,.4)
?x4<-c(.2,.7.,.3)


fun1<-function(x1,...){
?res1<-lapply(list(x1,...),function(x) -sum(log(1-x^2)))
?res2<-unlist(res1)
?res2}
?fun1(x1,x2,x3,x4)
#[1] 0.1451830 0.7440195 0.6306908 0.8084772

#or
fun2<-function(x1,x2,x3,x4){
?res1<-lapply(list(x1,x2,x3,x4),function(x) -sum(log(1-x^2)))
?res2<-unlist(res1)
?res2}
?fun2(x1,x2,x3,x4)
#[1] 0.1451830 0.7440195 0.6306908 0.8084772
A.K.








----- Original Message -----
From: Sara Farooqi <sffarooqi at gmail.com>
To: arun <smartpink111 at yahoo.com>
Cc: 
Sent: Sunday, October 28, 2012 2:39 AM
Subject: Re: [R] summation sign

hi Arun,
thank you for? email. No I want to repeat the sum 5 times. So i is 5
and hence there are 5 x-variables. Each of these x variables is a 3x1
vector for example.
So my question is how do I get R to repeat the sum 5 times and
recognize that each x is a 3x1 vector.
thank you!

On Sat, Oct 27, 2012 at 11:30 PM, arun <smartpink111 at yahoo.com>
wrote:
> HI,
> Your question is not that clear.
> Do you want to repeat the -sum() n times and then get the grandtotal?
>? x1<-c(.3,.2,.1)
> fun1<-function(x,n){
>? res<-sum(rep(-sum(log(1-x^2)),n))
>? res}
>
>
>? fun1(x1,5)
> #[1] 0.725915
>? fun1(x1,6)
> #[1] 0.8710981
>? fun1(x1,8)
> #[1] 1.161464
> A.K.
>
>
>
>
> ----- Original Message -----
> From: sffarooqi <sffarooqi at gmail.com>
> To: r-help at r-project.org
> Cc:
> Sent: Saturday, October 27, 2012 7:40 AM
> Subject: Re: [R] summation sign
>
> thank you vm for the reply! Just to make things a little more complicated
> --does the equation hold even if the values of x are unknown? More
> specifically perhaps we can still refer to the made up example
> Sum(n equal 5)log(1-xi^2)
>
> In the problem I am working on, I am writing a modified Newton Optimisation
> code with linesearch. Therefore the values of x are not given but each x
> variable is some nx1 vector ..e.g. lets take a 3x1 vector.
> So referring to this example, where we had to sum 5 times, how could I
write
> the function such that it sums 5 times, but each of the 5 x variables is
> taken to be a 3x1 vector.
>
> thank you very much again!
>
>
>
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/summation-sign-tp4647621p4647655.html
> Sent from the R help mailing list archive at Nabble.com.
>
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