using filter() to sum up

Hi,
I tried the formula

sum(psi*X[(t-1):(t-K)])

but it provides the vector of all observations. Thus, I changed K to k where 

K<-3 and k<-1:K

This yields better results but not what I want since I should get 3 values as K=3.

X[(t-1):(t-k)]

[1] 0.1
Warning message:
In (t - 1):(t - k) :
  numerical expression has 3 elements: only the first used

Why do I get this error message and how can I avoid it??

Thanks in advance


-----Original Message-----
From: peter dalgaard [mailto:pdalgd at gmail.com] 
Sent: 05 May 2015 11:41
To: T.Riedle
Cc: r-help at r-project.org
Subject: Re: [R] using filter() to sum up

Hi everybody,

I am trying to create a code for the formula in the attachment. I first tried following code:

ltau <- m + theta*sum(psi*X[t-k])

That's not going to work. It might work with something like

sum(psi*X[(t-1):(t-K)])

but it does not work and I get for X[t-k] every third element in my vector three times which looks as follows:
X[t-k]
[1] -0.25 -0.25 -0.25 0.50 0.50 0.50 -0.44 -0.44 -0.44 0.15 0.15 0.15

Thus, I tried the filter() function in R which looks as follows:
ltau <- m + theta* filter(f.USA$UTS, phi(K, omega1, omega2), sides=1, 
method="conv")

Reading the description of this function I am unsure whether this provides the sum of the k lags. The appreviation "conv" provides, as far as I understand, the moving average instead of the sum.

I would assume that it means convolution. Which is what you have in the formula.

Does anybody have an idea how the R code for the formula attached must look like? Is the filter() function appropriate?

It's barking up the right tree, but do your own checks...

-pd

Thanks in advance.
<tau.png>______________________________________________

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Peter Dalgaard, Professor,
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