[R] sum of variables in function

[beatleb]

Dear R users,

Probably, this is quite a simpe question, but I do not find the proper way
to obtain want I need. To explain the problem, I constructed a simple
example. 

Suppose I have the following function:

try1<-function(x){
y<-x[1:2]
z<-x[3:4]
y[1]*(z[1]+z[2])+y[2]*(z[1]+z[2])
}

This function will be part of a for loop. This is what I like to obtain for
every k:

if k=2
try1<-function(x){
y<-x[1:2]
z<-x[3:4]
y[1]*(z[1]+z[2])+y[2]*(z[1]+z[2])
}

if k=3
try1<-function(x){
y<-x[1:3]
z<-x[4:5]
y[1]*(z[1]+z[2])+y[2]*(z[1]+z[2])+y[3]*(z[1]+z[2])
}

if k=4
try1<-function(x){
y<-x[1:3]
z<-x[4:5]
y[1]*(z[1]+z[2])+y[2]*(z[1]+z[2])+y[3]*(z[1]+z[2])+y[4]*(z[1]+z[2])     
}

Assume that k will be quite high, for example 100. 
The problem isn't in defining a for loop, or in defining the appropriate y
or z, but in the line starting with 
y[1]. The values of the variables are still unknown, which causes that I am
not able to create this sum.

I really hope that there is somebody in the audience that can help me.



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