R help - Nov 2015 - summation equation whose numerator has subscript

Dear R experts 
Please do you have any idea about how this summation can be written in R(the
equation can be viewed in the following link):
http://s16.postimg.org/or2km30ph/equation.jpg 

I've tried out out this code but it gave me error for writing brackets in
function of summation:
>>> 
x=matrix(c(6,2,1),3,1) 

for (l in 1:3){ 
sum(sapply(1:3, function(j[l]){if(l>1){sum(sapply(1:j[l-1],
function(j[l]){x[j[l]]*(j[l]<j[l-1])}))}}))}>>>Thank you

I cannot understand that summation at all,  much less translate it to R. Do you
have an original citation for this thing?

As for putting subscripts in parameter lists,  that is not going to happen. You
have to accept that the code that calls your function needs to do any necessary
subscripting before it gives that piece to your function. Keep in mind that
apply functions do this by their nature without the mess of specifying it
yourself. If you know that the automatic subscripting that sapply does is not
going to get the result you want then don't use that function.
-- 
Sent from my phone. Please excuse my brevity.

On November 30, 2015 1:20:34 PM PST, Sherouk Moawad via R-help <r-help at
r-project.org> wrote:
>Dear R experts 
>Please do you have any idea about how this summation can be written in
>R(the equation can be viewed in the following link): 
>http://s16.postimg.org/or2km30ph/equation.jpg 
>
>I've tried out out this code but it gave me error for writing brackets
>in function of summation:
>
>>>> 
>x=matrix(c(6,2,1),3,1) 
>
>for (l in 1:3){ 
>sum(sapply(1:3, function(j[l]){if(l>1){sum(sapply(1:j[l-1],
>function(j[l]){x[j[l]]*(j[l]<j[l-1])}))}}))}>>>Thank you
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>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.
	[[alternative HTML version deleted]]

> On Nov 30, 2015, at 1:20 PM, Sherouk Moawad via R-help <r-help at
r-project.org> wrote:
> 
> Dear R experts 
> Please do you have any idea about how this summation can be written in
R(the equation can be viewed in the following link):
> http://s16.postimg.org/or2km30ph/equation.jpg 
Can you explain in natural language the goals of this expression. It makes
little sense to me to start with an index of j_sub_l = 0 and to then iterate to
up to j_sub_(l-1) -1 . How can there be a value for j_sub(l-1) with a starting
point of zero. The notation saying to do something for l = 2:n is not helpful
since values of ?l? doesn?t really appear in the looped expression (noting that
j_sub_l starts at 0, so it's not being determined by ?l".

I believe the confused notation was the cause of this question being closed
after it appeared last week on SO:

http://stackoverflow.com/questions/33882285/summation-equation-whose-numerator-has-subscript

And what intent is meant for the indices of the outer summation? The expression
j_sub_1 = 0 seems to have no corresponding reference point inside the looped
expression. So you would simply be summing the same value N times, but since N
is not defined we cannot write any code.
> 
> I've tried out out this code but it gave me error for writing brackets
in function of summation:
You should _always_, _always_, _always_ post the entire results of an error. We
have no way of seeing your console. Error messages are usually informative.
> 
>>>> 
> x=matrix(c(6,2,1),3,1) 
> 
> for (l in 1:3){ 
> sum(sapply(1:3, function(j[l]){if(l>1){sum(sapply(1:j[l-1],
function(j[l]){x[j[l]]*(j[l]<j[l-1])}))}}))}

You have three nested loops in the code above, but at least it appears you do
understand that R is a 1-based language. But since the image-expression goes
from 0 to some cryptic value (minus one) then the R version ought to go from one
to "one more? than that expression.

> >>>Thank you
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
David Winsemius
Alameda, CA, USA